Problem of the Two Doors: Classic Logic Puzzle

[@nigeria774]

"barbarian takes axe and kills first guard" "is he dead?"

[@copycruel]

U came from that video too?

[@redbaronmars4176]

@@copycruel we are sheep fr

[@talleywa5772]

Now you don't know what door is safe.

[@lordfarquaaaaaaaaaaad8311]

"No" "This one liar"

[@bearyvr6]

In this video the situation is stated that u can only ask 1 question

[@thomasgrable1746]

"One of us always tells the truth, the other one always lies." "Oh my god, Carl, I said I was sorry!"

[@calebwalters1869]

If one of them says this whole line then he gives away that he's the one that always tells the truth, because the liar would have to lie about how it works. Similarly if the liar says one of us 'always' lies, then he just told you that he doesn't always lie. But if the liar says that one of us always tells the truth, then neither of them will always tell you the truth.

[@Nuclearburrit0]

​@calebwalters1869 the lier gave the setup. Turns out both guards sometimes lie and both doors will kill you

[@w1ndgeneral226]

Barbarian takes his ax and kills the first guard. "Is he dead?" *"......no."* "This one liar."

[@princessmarlena1359]

Carl: “Oh, what a LIE! D’ooohohohoho!”

[@tclanjtopsom4846]

Seriously Flanders 😢

[@benji1901]

don't ask a question, just go to one door, open it and push the guard through. If you hear screams of death then that was the danger door.

[@davidtherwhanger6795]

That was my thought.

[@wesscoates5676]

Ahh, but what if you pushed the liar guard through the safe door, and he fakes the screams of death, thereby tricking you into going through the danger door?

[@davidtherwhanger6795]

@@wesscoates5676 Then just ask thru the door "Are you dead?" when the screaming stops.

[@wesscoates5676]

@@davidtherwhanger6795 uuuuuhhh... huh... that might work.

[@TheLifeOfKane]

The guard guards the door... your plan failed. Just ask him what the other guy would say, this isn't a logical PUZZLE its a kindergarten riddle

[@Smol_Schan]

This was very helpful. Usually I can never understand this riddle, but this helped me understand it.

[@BrainFoodforLife]

Soooo happy to hear this! Check out the new ones when you get the chance!

[@AdultToons]

Sometimes I need shit explained to me like I'm a newborn.

[@rogerkearns8094]

The words I've ever heard actually addressed to a newborn were, 'Breath, baby breath!' She was my daughter and she breathed just fine, as soon as she felt like it. :)

[@brigittakovacs7861]

'Takes barbarian axe kills one' "Is he ded"? "No" "This one lie"

[@KingOfSciliy]

Unfortunately, you still don't know which door leads to safety and you wasted your one question.

[@patrickrannou1278]

"Not problem!" Take axe to door. Grabs 2nd knight and throws him inside. If barbarian hears screamings: "Ah good me found danger door!"

[@Doctor_Straing_Strange]

but then you have no questions left to ask

[@vegaswithdrawal4132]

​@@patrickrannou1278Nope. The lying guard would fake his screaming, fooling you into thinking it's the death door when it's not.

[@cmonman7664]

But they are trained guards and would hack you. They wouldn't let you get close. Hence that's why they are guards

[@kevindomenechaliaga8085]

For those who didn't understand: Asking what door the other guard would tell me is safe, always leads to a false answer. If we ask the liar guard ¿What would the other guard say, if i asked wich door is safe? The liar guard would point to the damger door, since the other truthful guard would do the oposite. If we make the same question to the truthful guard, it would answer as the liar, and also point at the danger door. Thus, asking ¿What would the other guard say if we asked wich door is safe? always has the danger door as an answer. This way, we know wich is the danger door, and that the remaining door is the safe one :D I hope this explains it more concisely

[@matthewdavis9437]

It's guaranteed to point to the dangerous door, yeah. 😂 It's a good question.

[@howyoutubesmells]

you shold be the one who have made this video.

[@nagashtheforsaken]

Thank you! This video did a horrible job of explaining this.

[@khajiithadwares2263]

You include both the guards in the question since each have 50% chance of telling a lie, together they have 100%. So you get the wrong answer of whatyou ask. If you ask for safety you are pointed towards danger. If you ask for danger you are pointed towards safety.

[@mikehigbee2320]

Thank you. You explanation is comprehensible. The video, not so much.

[@theblackheart5727]

I doubt I’ll ever wrap my head around this conundrum. Thanks a lot Ricky, Steve, and Karl.

[@barukkazhad8998]

😂..feel the door to see if its hot

[@domatron1578]

Look lads ive got some post for God here

[@barukkazhad8998]

@@domatron1578 😆😆😆😆😆

[@barukkazhad8998]

@@domatron1578 a moronic genius

[@HelloThere.....]

You find a way to make them both say the same answer, IF they do so, then you know it's the opposite. The truth teller will accurately predict which door the liar will say is safe and that is always the danger door, and when that prediction matches you know that the liar was lying and that it's the opposite door. Remember you're not asking them each which door is safe, you're asking them which door they think the other will say is safe. By doing so you know that the truth teller will out the liar by correctly predicting his lie.

[@rabbithedragon]

This puzzle becomes next level when there's only 1 door 1 guard and he lies half the time but you get 3 questions to figure out weather it's currently safe to walk through the door.

[@maximized_1]

Does it like change to a dangerous one as soon as he lies?

[@kevindomenechaliaga8085]

He's playing this game on very hard mode 😅 I'll definitively give it a think ¿Do you have a solution? If you do, hats off 🎩

[@HansDelbruck53]

whether, not "weather".

[@wraithscythe1178]

Our astronomy teacher my sophomore year in high school gave us this problem at the beginning of the semester just for fun. End of the semester I figured it out for the whole class. One of the best teachers I ever had.

[@josephrusso4748]

The key factor that you omitted is that each guard knows that the other guard will respond in the opposite way. There are actually two ways of asking this question, you can ask about the door that leads to death which will reverse your response based on a yes or no answer. So there are two ways of asking this with 8 possible scenarios.

[@RectanerTreadway]

are you saying that the Liar would actually double-bluff?

[@josephrusso4748]

@@RectanerTreadway no because they have to lie, if they double bluff or lie about lying they would be telling the truth by default and also second guessing the lie

[@RectanerTreadway]

@@josephrusso4748 yes true. I get what youre saying now. One can either ask re: the door to heaven, or you can ask re: the door to hell.

[@artistpoet5253]

I thought the puzzle allows only one question to only one guard. You're not supposed to be able to cross check the result against the other guard.

[@n00blamer]

when you ask "what would the other dude answer" -kind of question you get both lie and truth in the spoken answer, the truth won't modify the lie it remains a lie so now you sneaked the lie to always be in the spoken answer. Since you know the spoken answer is always a lie you just take the other door.

[@Ozinarg]

This riddle is wrong. You get one question total, not one question per guard. Otherwise, you could just ask gaurd number 1: "whats 2+2?" If they lie, you know the other gaurd is the truth teller, and you can safely ask them which way is safe. If they do not lie, you know the other guard is the liar, and ask them which was is safe and then do the opposite of what they say.

[@ericbucher8636]

But you are still asking two questions.

[@G81L4L]

@@ericbucher8636yeah that’s exactly what he’s saying read the comment lol

[@taperhunter8671]

But you don't need to ask them both. He was just demonstrating that they would agree and you should pick the opposite.

[@TheShadowprototype]

The 2+2 doesn't work because you can only ask one question total, so you wasted your question. Because you weren't supposed to look for who's the one who lies, you were supposed to look for the wich door is safe. Let's say the danger door is left and safe one is right. "¿What would the other guard say, if i asked wich door is safe?" always lead to the same answer logically, wich the honest guard will respond with "the other guard will lead you to the left door (danger door)", meanwhile the lying guard will respond with "the other guard will lead to the left door (danger door)" so you know you should do the opposite thing because BOTH say, since the answer will always be the same one. Even if you ask wich door is the danger door, they both will "agree" with the other. It was never crucial to know wich one is the liar, but to find wich door is the good one

[@mkultrak8226]

Thanks, I was lik huh

[@luiginishimura]

When I first learned this riddle, I learned a different answer. You ask either guard 'What would you say if I asked you which door was safe?' The honest guard honestly tells you which is safe, because that's what he would say if you asked him. The lying guard will give you the right answer because he's lying about the wrong answer.

[@BrainFoodforLife]

Same logic no?

[@RoderickEtheria]

Yes.

[@patrickrannou1278]

Many D&D RPG players know this riddle. So I made the room with two undead knights, and an undead priest. The undead priest is the one presenting the riddle. So the players assume the typical two doors puzzle situation, so ask the question the "good solution" way, asking one knight what the other knight would say. If they try to ask the priest he says he doesn't know which door is the safe door. So they get a door that they "logically" think is the safe one, and go there. However, their entire premise is wholly faulty: Nothing proves to the players that the undead priest is actually telling the truth about the entire situation! In fact the 3 undeasd can say whatever they want! Both doors simply lead to more dangers, and the "good solution" of assuming the undead priest said the truth, actually leads to the worse of these two rooms. The 3 undead in the room know they can't beat the PCs directly in a fair fight, so they hope to avoid direct combat until the PCs have to start facing the threat of one of the next rooms, and then quickly arrive to attack the PCs "in their back", while they are already busy fighting! Suddenly making the fight way tougher. The only "hints" that the PCs should not believe the priest, is a previous encounter with the same type of undead knights (they all have the same heraldry symbol on their shields armor robes and vestments), to show how lying, cunning, and manipulative, such undead can be, with that 1st undead trying to befriend the PCs, offering to act as their guide to lead them to the treasure "if they then promise to bring him to a holy temple so he can be buried with the proper blessings and rituals so his soul can find peace" (a load of BS). But then he leads them straight into some deadly trap, that he activates directly himself, by pulling a secret lever, and then attacks them while insulting them for being "such stupid naive suckers". Plus 2nd hint the history analysis of their heraldic symbol reveals that that their clan of knights got cursed to undeath because they were super evil. So the "true" proper way to handle the "two doors puzzle room" is just to directly attack the 3 undead. I can make OTHER puzzles, but the 2 doors one is just so well known in the gaming community, it is better to use it as a red herring lol. Basically the big lesson is "Don't thrust monsters!"

[@Pelerin985]

"Do you have your helmet on your head right now?" "No." "Thank you to be such a good liar."

[@NovaBoiii]

Fr, it’s so simple

[@davidjones-vx9ju]

@@NovaBoiii yea... so which door is safe?

[@NovaBoiii]

@@davidjones-vx9ju Ask them 🗿 You know which one lies and which one doesn’t

[@davidjones-vx9ju]

@@NovaBoiii you only get one question

[@KingOfSciliy]

@@NovaBoiii Just finding the liar doesn't mean you've found the door that leads to safety. It was never established that the liar automatically guards the danger door and vice versa.

[@eskailerwhite.7593]

😪 i still cannot understand

[@RectanerTreadway]

Rules: Guards are identical, although technically this does not matter for our logic, it helps to envision them this way to grasp the set of variables in this equation. Only they know who is the Liar and who is Truth. Only they know who is guarding the passage to paradise. It is not at all guaranteed that the Liar guards hell, nor that Truth-teller guards paradise. You must also basically assume that the Liar intends to see you pick “the bad door” because in the roles of this puzzle, your own role is defined as you intending to pick the “good” door i.e. "Get out of the Dungeon". The conceit of the puzzle is that having a Liar involved at all presents the main conflict for us. We must neutralize this conflict somehow. The goal is not to *fixate* on the liar and figure out who is who; the goal is to formulate a question that *reduces* the odds. A question that makes all the variables "non-randomized" but a better way to state this is, "to make all these variables incriminate the same culprit". Game: Scenario to prove the theory Theory 1 - Honest guard in front of Hell. (To be known as Door U for Undesirable in our process of elimination. The door to paradise will be known as Door Y for YES.) You can’t just ask the Honest-Guard if he’s guarding paradise because you must assume that he could very well be lying. And you can't just ask him "what am I wearing?" or something redundant, because even if you prove that he's a liar, you still haven't proved that he is guarding the door that you need to select. So, here we are, there's two inscrutable guards in front of two indiscernible doors, and I have no choice but to decide randomly who to ask a single question. A. If I end up asking the HONEST guard “what would the other guy tell me to pick” he’d tell me *honestly* that the “other guy” would tell me *dishonestly* to choose his door aka Door U. -- This is logical because he's telling us that the Liar would want us to choose Door U (which both guards know as being Hell, and the Liar is interested in foiling our plans because I guess our enemies hired him to do that). B. If I end up asking the LIAR (still unbeknownst to me his credibility) and ask same question "what would that other guy tell me to pick", he would default to his duty of lying, and tell me *dishonestly* that the other guard would "Pick His own door" aka Door U, again. Theoretically, this is dishonest because all we are allowed to assume via our theory is - that whoever the honest guard is, he would never advise us to pick Door U if we asked him directly. In other words, we need to assume if the honest guard is ever asked "what door should I pick" he will always tell us "the truth" aka technically "our truth" aka "the thing we want" aka Door Y. While we cannot actually prove on-the-spot that the liar is lying, the phrasing of the question against the available facts allows us to eliminate 1 perilous door from our choices, no matter which guard we end up asking. Because the fact that the liar will exclusively provide misinformation is exactly what our clever question is taking advantage of: It's this process of elimination which means that "a second question" is not required. It is true however, that in the reality of this scenario, order to pick the right door, you MUST first ask the question. The question is required because it helps us receive more concrete data, and it's only with that new data can we THEN make our logical deduction. Therefore via the process of elimination which is now possible, you can determine that the other door, aka the only other door in front of you aka Door Y; is your remaining selection. So to summarize; in both instances, Door U is alleged as the door to choose. No matter who I end up posting the question to, in both cases Door U will be alluded to, because in both cases the Liar will be responsible for tainting all the available data, giving you the opposite of what youre searching for. Knowing this, you also deduce that you must choose the opposite door from what is told to you "as conjecture", after asking that question which theoretically forces either of them to acknowledge an opposing factor, and thus both will indicate the exact same door.

[@eskailerwhite.7593]

@@RectanerTreadway what a deep explanation, thanks bro!

[@RectanerTreadway]

@@eskailerwhite.7593 i was stuck on this for a while myself so I understood your pain and wanted to alleviate the suffering if possible

[@ulfberht4431]

Basically the answer is this: the guard that tells the truth would give you the answer of what the other guard would say which is the wrong answer since the other guard is a liar and the one you asked is the truthful one. In essence, he’s giving you the answer of what the other would say. The guard that lies knows the other will tell the truth and since he lies he will give you the wrong answer as well because he’s a liar and that is not what the other guard would say. In conclusion, the answer will always be the opposite of what the guard said, no matter which one you ask.

[@natas9967]

You and all of us..

[@wubuck79]

This has been probably my favorite riddle or brain teaser since a pastor told it to me almost forty years ago. I was about eight years old and when he told me the answer it kind of blew my mind at the time lol

[@mingmanangan]

if i ended up in that situation... i'll just go home and won't bother those guards :)

[@RitsuSakuma69]

*You are literally in prison, stupid. Your only way HOME is through the door!*

[@fshjgsfhhgshjfhe]

Its really easy if you get the jist of it, alternatively you can kill them both but that would not be very nice to mr. honest.

[@LNC4P]

Thanks for explaining the riddle from "The Labyrinth"!

[@BrainFoodforLife]

Glad it was helpful! I'm a sucker for these.

[@RoderickEtheria]

Labyrinth has a broken form of the riddle, as they break the rules of the riddle while getting the information for the riddle out.

[@Мопс_001]

Basically the point of the riddle is to make a question that would result in the same answer from any of the guards. And at the same time this question gives us the answer to the riddle. So the only way to do it is to "connect" the guards to each other by the question

[@hobowithawaterpistol9070]

But the narrator doesn’t tell you which one is lying and which one is telling you the truth. Without that info it’s 50/50!

[@Мопс_001]

@@hobowithawaterpistol9070 I advise you to watch the video again

[@BloodyAlex92]

"How many fingers am I holding up?"

[@BrainFoodforLife]

Only one question

[@KingOfSciliy]

Plus, you've only found the liar. You still don't know which door they are guarding.

[@G81L4L]

@@KingOfSciliythat’s what the reply is implying bruh

[@RoderickEtheria]

​@@G81L4Ltruthteller is not necessarily guarding a specific door.

[@RandomsFandom]

You dont ask the guards about what is behind them, you ask them about what is behind you.

[@Cinnamon_Rolls_Out_Of_The_Oven]

But then you don’t know which door is the death door and life door

[@RandomsFandom]

@@Cinnamon_Rolls_Out_Of_The_Oven you must first determine which one lies, then you can ask about the door

[@Cinnamon_Rolls_Out_Of_The_Oven]

@@RandomsFandom the whole point of the riddle is you can only ask them both one question.

[@MasonMcLeodFilms]

@@Cinnamon_Rolls_Out_Of_The_Oven Dude tried to be all 500 IQ Batman Professor X but just completely missed the point of the riddle lol

[@hobowithawaterpistol9070]

@@RandomsFandomYes, thank you! That’s what I say! It’s an impossible riddle! The odds are 50/50!

[@PhilipPerez-PLC]

I thought you can only ask one question, period. Not one question to each guard, for a total of two questions.

[@madnessbydesignVria]

It is one question: "What would the other guard say is the danger door?" The liar will lie, and the truthful one will answer as the liar would, thus both giving the same answer - the lie. Then you go through the other door.

[@stevemorse108]

I loved this conundrum when I was nine years old. I didn't do too well at school but then I did very well in my university entrance exams and went on to graduate from a top university with a GPA of 3,8....I did well at high school with lateral thinking problems ....I wish that I had had more confidence in my intelligence when I was at high school.

[@zg3671]

Finally, after all these years, that episode of Yu-Gi-Oh now makes perfect sense to me. Ever since watching that episode I thought it was madness but alas it was shear brilliance and you explained it so simply and elegantly. Well done ✅.

[@jemandoondame2581]

Which episode is it?

[@AlexiosKasagiannis]

@@jemandoondame2581its somewhere in duelist kingdom

[@SilverBolt316]

​@jemandoondame2581 its in season 1 where yugi & joey duel he paradox brothers its part 2. and i was thinking the same thing

[@unexpectedTrajectory]

You can also ask a hypothetical: "If I asked you if this was the door that leads to death, would you say yes?" If it is the door that leads to death, truthful will say yes, but liar will also say yes, because he is lying about the answer he would give you (a double negative) - "Yes, I would tell you yes (not true), this is the door that leads to death," getting him to lie about his lie has forced him to tell the truth. The same works in front of the safe door, where the same question will make both of them say no.

[@moixemi]

but u don’t know who the liar is?

[@tclanjtopsom4846]

A double negative only applies to maths.😂

[@nagashtheforsaken]

I see a lot of people not getting the riddle. Part of this is because it's horribly explained in the video. First off, the guards can't speak except to answer one question (not one question each). So the instructions to the riddle have to be given by a third party, or a message on the wall or etc. Second, this riddle involves two riddles in one, really. You have to determine which guard is lying, and which door is safe, and you only have one question. By asking either of the guards "which door would the other guard say is safe", you solve both riddles in one question. In either case, whether you ask the liar or the truthful guard, and no matter which door they guard, they will always pick the same door. So you can ask either guard the question and choose the opposite.

[@hobowithawaterpistol9070]

The biggest problem in this riddle is not knowing which guard is the liar and which is telling the truth. With that knowledge, you can then ask a trick question.

[@cmcollis]

Bro, Sarah taught me all I need to know here.

[@kevinogill6726]

Easy. Ask either guard which door the other guard would say is safe. Then choose the opposite

[@annonymousannonymous9586]

I remember seeing this logic puzzle in both Samurai Jack & the OG Powerpuff Girls series.

[@TheTSense]

"Is that a shield you have there?" "Is this door the safe way?" If the first guard says he has a shield, the other has to say no.

[@tomosjackson4760]

But you can only ask 1 question, so how can you know what they both agree on?

[@AnthonyWilliams-bp5mn]

The question was if you were the other guard what would you say. The truth telling one would say the other guard is safe while the liar would say he’s is safe. That’s in scenario 1 if the truth one is guard the safe path and the lying one is guarding the certain death path. Based on that logic you would not only identify who’s the liar and who’s telling the truth but you would know not to pick the path they both say.

[@dariusq8894]

Anyone else get "Labyrinth" flashbacks? 😂

[@pyrrhicvictory6707]

I'm amazed so few people got the reference.

[@riact123]

Yep! The moment I saw the thumbnail, I thought of Labyrinth.

[@bassage13]

@@pyrrhicvictory6707 It's not a reference to Labyrinth. It's a very old puzzle. Labyrinth referenced this well known puzzle.

[@pyrrhicvictory6707]

@@bassage13 Fair enough but I bet it was popularised by Labyrinth

[@dannybursace9151]

I clicked on this earlier today & watched Labyrinth later on…I could not believe it..never heard of this puzzle before then twice in one day…life is weird like that sometimes

[@wrg1183]

Easy! Ask both if they will walk through the door first, before I have the opportunity?

[@LJLMETAL]

You can also ask which door would the other guy say would lead to certain death.

[@davidjones-vx9ju]

this is making the assumption that each guard knows that one lies

[@wenaolong]

You could even just ask either guard whether the other guard would answer that the door he guards is safe. If it isn't, then either guard would answer "yes", if it is, then either guard would answer "no". In the former case, you go through the door behind the guard to whom you are posing the question, in the latter, you go through the door about which you are posing the question. When the guard you ask says "no" about what the other guard would say concerning whether his door is the safe door or not, you go through that one. If he says yes, that's the wrong door. This works whether the guard you ask is a truth teller or a liar, and you need ask only one question: "If asked, would the other guard tell me his door is the door to safety?"

[@ZeldaSam1]

The logic of this riddle will always elude me.

[@BrainFoodforLife]

Watch to the end and all is revealed!

[@kazekagekid]

“Are you a guard?”

[@tigrenaranjo]

How would this question lead you to know which door is the safe option? With this question you only know who is lying and who isn't, and as you only have one question, this doesn't answer which door is safe

[@kazekagekid]

@@tigrenaranjo”you can ask one of them only one question” is not violated by asking them to answer two different questions, one each. his solution asking the same question may be more elegant, but mine’s cleaner, and he didn’t state that limitation in the prompt as clearly as when he’s working through it. he arguably violated his own prompt if you’re going to be that pedantic, since he had to ask both guards a question anyway.

[@kazekagekid]

@@tigrenaranjoalternatively, you can also figure out the answer to this general riddle with one question if you’re listening carefully and given the prompt by one or both of the guards. the one who says they are guards or guarding a door is 95% the truth-teller unless they’re not actually guarding anything.

[@kaptainkittens583]

@@kazekagekid I think the implication is pretty clear you could only ask one question, to only one guard, to determine which door is safe, and the answer he gives in the video does not violate his rule; he simply demonstrates the answers each guard would give for each scenario to cover the possibilities, and that no matter which guard you ask or which door they are in front of - you only need to ask one of them and always choose the other door as the safe one.

[@kazekagekid]

@@kaptainkittens583​​⁠ “you can ask one of them only one question” 0:37

[@andrewg.carvill4596]

The classic problem has one unstated assumption, namely that the guards both know about the other being either truthful or a liar. If they didn't know each other, the truthful guard would truthfully answer "I don't know which door the other guard would tell you is safe" while the lying guard, it seems, could not give any logically coherent answer to the question.

[@vegaswithdrawal4132]

This is a setup, both guards read their roles for the day before clocking in to work. If they don't play along, or screw it up like morons, they will be terminated immediately. 🔥

[@deanstanley2125]

How would the guards enter the dungeon? They would have to come in through the safe door so by observing them entering you have your answer

[@BrainFoodforLife]

Interesting hijack of the task Captain Kirk but this ain't the Kobayashi Maru! hahaha

[@dominik94rausch]

One always tells the truth, the other one never lies.

[@RecordSlowrun]

Simple solution: “Is the lying guard in front of the door to safety” Honest guard in front of door to safety: No. Honest guard in front of door to death: Yes. Lying guard in front of door to safety: No. Lying guard in front of door to death: Yes.

[@lusterlessnova3199]

How do you know which guard is the lying guard tho?

[@JustSomeKittenwithaGun]

​@@lusterlessnova3199Check their comment again. It gives the same outcome for the corresponding door regardless of who is by it.

[@lusterlessnova3199]

@@JustSomeKittenwithaGun I don't get it. -Edit Ohhhh. It's not about knowing who the lying or truthful guard is, but the answers they give. "No" leads to safety. Appreciated~

[@safetybeachlife]

The door to safety is always the guard who says “No” Or the other door to the one who says “Yes”

[@Chaytonioio]

@@lusterlessnova3199 I'll try to give my understanding of their comment so you'll hopefully understand it better. If either guard said no, you should go through his door regardless as the other comment described. If either said yes, go through the opposite door. Why? Remember, you only need to ask that one question to ONE guard only, but this still works if you're allowed to ask them both the same question. “Is the lying guard in front of the door to safety?” Guard says NO: If they're the liar, the actual truth is "YES". The other guard MUST say no as well because otherwise there would be 2 lying guards. You can safely go through this door. “Is the lying guard in front of the door to safety?” Guard says YES: If they're the liar, the actual truth is "NO." Again, the other guard MUST say yes or he'd be a liar as well. Go to the opposite door of the guard you asked. Basically, you know which guard is lying because this question is really good and non-contradictory. However, this is a contradictory question IF this condition is met: If you asked them this specific question and one guard said yes, but the other guard said no it contradicts this question and this forces the truthful guard to lie. Understanding this potential paradox is pretty helpful in understanding the solution. If they both were to say no (or yes) at the same time to the question, then we know for a certain it isn't contradictory. Well, I hope this didn't confuse you even more. I had to think pretty hard about it too.

[@kevinpitts22able]

1 question: “Would each of you walk through your respective doors, wait 5 mins, and then come back out please?” The one who comes back out has the Safe door.

[@SuddenReal]

"No..." "A-HA! This is the truth telling guard and it's the bad door! I go through the other doo-AAAAAaaargh..." "No, I'm here to guard the door, dumbass, not to do your bidding. What is it with people and their entitlement, right George?" "I thought it was pretty smart." "Well said, George."

[@williammeyer2584]

I thought you could only ask one question between the two of them, not one question for each guard?

[@samuelfernandesoliveira]

It's just showing what would happen per scenario. If you asked the liar if his door was safe, (and it waa dangerous) he would say yes. The same would happen to the truthful one.

[@robbie_the_mastermind2176]

Walks up to one of the guards and sniffs ‘Did you poop your pants?’

[@RTtheGamer08-RBLX]

*takes rock, throws it at one guard* "Did I just throw a rock at you?"

[@TuranTahaAli]

I think there is kore than one way to solve this. My way is asking "Is there a truthful guard standing at the safe door?" and pass through the gate of the guard who says yes.

[@robbie_the_mastermind2176]

If there was one guard named Kairos Fateweaver, ask him any questions and he would will give you three answers, all of which are true, and horrifying to know."

[@Horntsnest1]

in the end you still asked two questions... am I wrong?

[@TheFilipFonky]

You are wrong. You ask one guard "what would the other guard say is the safe door?" and then you do the opposite of whatever answer you get. Just one question.

[@tohian]

@@TheFilipFonky Actually, OP is right. If you listen to the video at 3:00, the narrator clearly says “you have to do the opposite of what they agree on”. But in order to know what the guards agree on, you have to ask 2 questions. So this question is somewhat flawed.

[@RectanerTreadway]

@@tohian the narrator here is implying that they would *theoretically* agree on the same door if asked the same singular question. in other words, you only need the 1 question to prompt them both into giving you the same response meaning no matter who you ask, you can safely assume what the other will say

[@zdzdhhfdzhzdhdzheherh33]

@@tohian it's not. They would always agree on the same door.

[@Amaipuppy]

They would both answer at the same time but you still get the right answer, so it's one question.

[@tegathemenace]

Finally one I can get my head around If I asked you the question "are the two guarded doors safe" would your answer be yes?. Case 1: The doors are both safe. The liar's answer to the inner question would be no. And he would lie that his answer would have been yes by saying yes.(Yes my answer would have been yes) His polar opposite would have an answer of yes to the inner question and his answer would also be "Yes my answer was yes". Which means if both doors are safe the answer is YES from either guard. You can now enter either guarded of the two doors. Case 2: One door is unsafe Given it's an "AND" question if it isn't Case 1 it's automatically Case 2. Not Case 3(none of the two are safe) because if that holds that means the 3rd is the only safe door. 2 doors have to be safe according to the rules. Moving on, either guard will answer NO if it's a Case 2 (use logic in case 1). If one of the doors are safe it means the other is the safe one. Which? Unknown. But no you are sure the second safe door is the 3rd This is built on : Double negative and Double positives are positive. (- × -) = (+ × +) = +) Instead of asking how the other would respond. I asked the guard how he himself would respond. I wish I could come up with the easy answer tho😂

[@123Mathzak]

Ask the guards if theyre a guard who’s guarding a door, and go with the guard who says yes because obviously the guard who says no is lying.

[@hobowithawaterpistol9070]

You can only pick one guard and ask him a question. You can’t ask them both!

[@DuckTheAssasin]

​@@hobowithawaterpistol9070 Wrong, You can ask both guards the same question, but you can only get one answer from each.

[@shawbag11]

Easy puzzle just ask if i was to ask the other guy what door to go though what would he say. then u just do the opposite of whatever they say since both guards would agree on the wrong answer.

[@RandomsFandom]

Third option. Go through a door at a 50/50 option

[@Dethneko]

Ask one guard, "If I ask the other guard if this door leads to safety, what would he say?" Way I have it figured, if the guard says "yes" then the door leads to doom, and if the guard says "no" then the door leads to safety.

[@hobowithawaterpistol9070]

But which guard is the truth teller and which is the liar?

[@Dethneko]

@@hobowithawaterpistol9070 -- The point of the riddle was to find the safe door, so this question won't tell you whether he's the truth guard or the liar guard. If you want to know who's the liar, there may be a loophole you can exploit. You could ask, "Just to clarify, you're telling me if I asked the other guard if this door lead to safety, he would say '___'?" and you fill in the blank with 'yes' if the guard said yes, and with 'no' if the guard said no. As a question of clarification you aren't technically asking for more information, but rather repeating the same question asked altered only to include the original answer. As it is still a question, if the rules are strict you may be met with silence and never know. However, if they are lenient to questions of clarification they may be compelled to answer. If they do still answer, well, it is a yes or no question, so their compulsion should still apply. meaning if they answer 'no' they are definitely the liar, however, an answer of 'yes' does not guarantee the truther. If there is a loophole in the rules that allow you to ask questions of clarification, there could also be a loophole in the rules that compel the liar to break his initial compulsion, and answer them honestly.

[@hobowithawaterpistol9070]

@@Dethneko I can’t remember if I brought this up or not, because my head was starting to spin, but a riddle should have a definitive answer to it! A riddle such as “If a tree falls and no one is around to hear it, does it make a sound?” This is a philosophical riddle wherein the riddle is constantly debated. My point being that the riddle of the two doors given by the host clearly states in the beginning that there is definitely a door leading to safety, and a door leading to death! This means there is an answer at the end of this riddle. It’s the participants job to figure out how to find the right door by asking the right question. I look at it this way, if a man is hosting a shell game say in NY and he tells you to find the pea under one of the 3 shells as he moves them around. He’s quick, he talks fast, you bet money and you guess which one the pea is under when he stops. Win or lose, there is actually a pea under one of them. That’s what makes the challenge! If he removed the pea without telling you and then asks you which one is it under, then he’s just a con man and there’s absolutely no challenge and no real game to be played. That’s what’s happening here with the 2 doors! If there in fact is one door that the pea (safety) is behind then in this case it either has to be behind door A or door B or for viewing sake the left or the right. If the possibility of the safe door can be either left or right depending on who you actually approach to ask the question, then it’s like the answer can travel. Here’s a much simpler example of my point: My hands behind my back and I put $20 in one hand and told you to guess left it right, no matter what you answer I’m going to move the $20 to the other hand. This I why I say the riddle is flawed.

[@Hadouken9000]

"One can only tell the truth, the other can only lie." All right, so tell me the color of my shirt.

[@themoretruthfultruth]

This one is so old. Why did someone even bother to make a video about it. This riddle was even in the movie Labyrinth.

[@paulgreen9059]

Ask "If I asked you 'is your door safe?', what would you say?" That would work unless the guard got confused, I suppose.

[@NotFoundead]

I can't! I really can't! People not understanding this even after the explanation just blows my mind away. It literally took me 5mins to solve this. Seems like critical thinking, following simple rules and use of logic is not a thing anymore. You can ONLY ASK 1 question to ONLY 1 of the guards. So, you ask one of the guards (doesn't matter which one) something like: "If I were to ask the other guard which door is the correct one, what would he answer?" If you ask the truth teller, he's gonna tell you the wrong door (because that's what the liar would answer). If you ask the liar, he's also gonna tell you the wrong door (because that's the opposite of what the truth teller would answer). By knowing this, you don't need to ask the question to both guards. You don't even need to know which one is which. Since the outcome is the same in both scenarios, the other door will always be the correct one. Side note: Asking for the wrong door, would also work, in that case you'd pick the same door as the guards. Literally the same, but reversed.

[@n00blamer]

Simpler way to think about this is that the spoken answer contains what either guard would have answered on his own, in other words... the spoken answer IS ALWAYS A LIE because one of them is a liar, we simply guaranteed that the lie is always in the spoken answer.

[@hobowithawaterpistol9070]

@@n00blamerWhy would we assume the truth teller would not speak the answer?

[@n00blamer]

@@hobowithawaterpistol9070 I didn't say he wouldn't, both would answer whatever question you ask is a given in this puzzle.

[@hobowithawaterpistol9070]

First of all just because you think you figured it out doesn’t mean you’re better than others because they can’t figure it out or they take a while to! Every body learns at a different pace! Second, it appears to me that while the outcome may be the same as you say, there’s no possible way of you knowing which door is safe if you don’t know which guard is the truth teller and which is the liar! You are still at 50/50 without that information! If I’m wrong, then please tell me is it door A (left door) or door B (right door), and please explain how you know that!

[@n00blamer]

@@hobowithawaterpistol9070 I know which door is a safe because whichever guard I ask, the answer contains a lie. I ask "what would the other guard say about your door, safe or death?" It does not matter which door I am standing in front of, or which guard is at that door. If the guard I ask is a truthful he will say truthfully what the other guard would say, the other one would lie and this guard will then tell what the liar would answer so the answer must be lie. If I ask the liar guard he would lie what the truthful guard would have answered so the answer is again a lie. This way the answer is always a lie no matter which guard you ask. So, if I am in front of safe door the answer would always be it is death door. If I stand in front of safe door the answer would always be it is the death door. So I know which door is which. I come back to what I wrote above: the spoken answer always contains a lie because both guards answers are combined. Truth is always truth, a lie reverses the answer.. there always is reversion because we ask what the other guard would say, so both lie and truth are combined. Truth won't change lie, and lie changes truth.. so answer is always a lie. Another way to think about it is that truth is positive (+1), and lie is negative (-1), answer is +1 * -1 = -1, answer is always negative.. negative means lie and positive means truth.

[@michaelannen4168]

"Is your door made primarily of wood? - solved

[@reinotsurugi]

Thanks you! The illustration really helped.

[@idontanswerquestions9879]

What’s 2 + 2?

[@Tovek]

The door is a lie. You are in the safe room and the two guards are your new food source.

[@RecklessFables]

A mistake many riddlers make is when they state the puzzle, they have one of the guards as the speaker. This breaks the rules of the riddle unless the truth guard is the speaker... which also breaks the riddle.

[@thetruth3611]

But you are assuming that the guard on the right is honest. You wouldn't know.

[@vandaahll]

How can we do the opposite of what they agree on when we can ask1 guard 1 question?

[@BrainFoodforLife]

Phrasing

[@madnessbydesignVria]

It's not that they agree, it's that they will, by their nature, give the same answer. Asking what the 'other one' would say means the liar will lie, and the truthful one will honestly tell you the lie the other on would say - resulting in the same answer, so you only need to ask one. The answer will be a lie, so you do the opposite.

[@TheoneGodfather]

One question for each guard helps.

[@hobowithawaterpistol9070]

This Riddle is flawed because it does not tell you which guard is honest and which one is lying. Therefore trying to trick one guard or the other is impossible if you have no idea which one is the truth teller and which one is the liar! If I try to use trickery it doesn’t matter! Gordon Gekko said it best “Information is the greatest commodity I know of!”

[@BrainFoodforLife]

That’s the entire point.

[@madnessbydesignVria]

It doesn't matter which one is lying, you need to know which door is safe. By asking what the other guard would say, you insure getting the lie, and do the opposite.

[@Njorl]

You can do this with one guard. State that the one guard either always lies or always tells the truth. Then ask, " If I were to ask you which door leads to safety, which door would you indicate?" Note, you are NOT asking which door leads to safety. You are asking how they would answer if they WERE asked that question. If the guard always tells the truth, then obviously he will point to the door that is safe. If the guard always lies, he will first consider what he would answer to "which door leads to safety?" If he was asked that question he would lie and indicate the unsafe door. However, to answer the question that is actually asked he has to lie about how he would answer, so he indicates the safe door.

[@princessmarlena1359]

And whatever you do, never say “It’s a piece of cake!”.

[@BWills32]

So for the favorable outcome, do the opposite of "what the other guy would say?"

[@anthonyju6392]

Dr. Who. I remember the solution to this problem so long ago.

[@andreasmartin7942]

'Is the liar guarding the door to outside'. Pick the door with the guy who says 'no'.

[@BrainFoodforLife]

That’s part of the challenge. Figuring it out 👍

[@crismon0726]

me: pushes a guy me again: did i push you?

[@alaxsparkz359]

For anyone else who was challenged on the logic of the answer like I was. The simplest explanation is if you ask the question to the truth teller he’s not going to point at his door so you know his door is safe. If you ask the liar the liar will point to his own door meaning the other door is safe. So basically the question forces the guards to point to the wrong door no matter what.

[@thomasm.6352]

Whoever explains the rules is the honest one. And will get you to safety.

[@nagashtheforsaken]

The rules are not supposed to be given by the guards. A third party is supposed to tell you the rules, or they are displayed by a tablet, scroll, or message on the wall. The guards can only speak to answer one question.

[@worldbard1370]

Both the guards want you to think the other is true to kill you, if you ask "would he tell me to go through door 1" and they say yes its because they want you to think the other guard would send you to your doom

[@slayer8actual]

I have one question. It is divided into 32 subparts and will require you to show your work.

[@BrainFoodforLife]

😆

How many fingers am I holding up?

[@GDAccelerate]

the answer is obvious, the person who said “One of use tells only the truth the other lies” is the truth teller

[@TheFinalChapters]

1:00 Oh, if The Labyrinth is any indication, there is no such thing as "absolute" certainty.

[@melabec]

In the movie Sarah gets it right. But she keeps taking the Labyrinth for granted and doesn't respect the dangers there. She gets punished every time she calls it "A piece of cake." It is at that moment she falls. She did not die and was able to escape with Hoggle's help. So obviously the door she went through did not lead to "certain death".

[@Virtue2721]

My question would be "Whats 1+1"

[@nicholasmuro1742]

That would help figure which guard is which. But you only get 1 question. So you still wouldn't know which door.

[@Virtue2721]

But you do. The guards each guard one door. once you know who know is lining you automatically know the door. knowing the guards is the same as knowing the door in every iteration of this puzzle. some people have tried to overcomplicate it desperately trying to add more variables but math really is the answer here.

[@TriAzF]

@@Virtue2721”once you know the guards you automatically know the door” This is incorrect. The guards could each guard either door, so knowing which guard is which only helps you determine if their answers are true or false. But you already asked a question to determine this, so knowing the guards are meaningless since you can’t ask anymore questions.

[@ericbucher8636]

Just randomly select a door and go through it. We are all going to die eventually.

[@saintmateo]

Me, blowing my one question just to vent: "Dude, there's probably a dragon or something at the end of this dungeon anyways, so even if I pick the right door my odds of survival are not great. Does it even matter to you if I die in the next room or if I die to the boss at the end?" The guard: "Wow, I'm supposed to be the liar but that is a bleak perspective to share. Now I feel bad, here, take these healing potions in case there is a dragon."

[@BADD1ONE]

"Are you a gaurd standing infron of a door" bam

[@jellygodgames2139]

Go up to the first guard and ask, how many fingers am I holding up? Let’s say you’re holding up two, and the guard says three. Then go to the other door and ask, is this door safe? If he says yes go through it, if no don’t go through it and go to the other door. If the first guards says, 2 fingers, that means he is telling the truth. Go to the next guard and ask if the door is safe, if he says no go through it, if he says yes go to the other one.

[@mariosebastiani3214]

only 1 question allowed, not multiple ones

[@jellygodgames2139]

You can ask each of them one question, my question to the first guard is the fingers one, my question to the second guard be about if the door is good or nah

[@TriAzF]

@@jellygodgames2139You can ask one question period. Not one question to each. This video words it a bit weirdly but the problem is based on only have one question. If you could ask 2 questions, than yes your solution works (or any solution where the first question just verifies one of the guards identities), but it is barely a puzzle at that point.

[@jellygodgames2139]

@@TriAzFyear ur right he just words it weird

[@taxman_torched]

Is the sky blue? He asked

[@SKIT..CENTRAL]

But I thought only 1 of them could answer you so if only 1 can answer then the other won't say anything to help you figure out which is lying and which isn't

[@benji1901]

It's still the opposite of the answer whoever you ask. Door 1 = safe, If you ask true guard what the liar guard would say, the liar guard says door 1 is danger; danger being the opposite. If you ask liar guard what door true guard would say, he would lie and claim true guard would say door 1 is danger; danger being the lie. Both answers are door 1 = danger, which is the opposite of what is it. So even though you ask one question you can automatically just do the opposite of the answer.

[@RoderickEtheria]

I can beat this riddle with only a single guard stationed, so long as truth and lie are the only options. "Which way would you say leads to freedom?" is sufficient. If it is a lie, the guard has to lie about the falsehood he would tell you, producing the truth. If it is the truth, the guard will tell you the truth about the truth he would tell you. Either way points you to freedom.

[@JonCox-hp4fw]

I read a riddle about this sort of thing many years ago, and the answer is much easier than you make it sound! You just go up to one of the guards and ask "If I were to ask you if this door lead to safety, would you say yes?"

[@n00blamer]

The trick is to have both guards answer the question, this is done by asking either guard what the other would answer.. now you would know that the answer always has a lie in it. If you ask: "which door would the other dude say is the safe one?" or "would the other dude say THIS door is safe?" .. whatever the answer is, you know it's going to be a lie.. so you take the other door and go watch netflix and chill.

[@JonCox-hp4fw]

@@n00blamer Think about it! If I ask the liar who is standing in front of the death door, "If I were to ask you if this door leads to safety, would you say yes?" His response is always a lie! If I ask him if he would SAY yes, He would lie about the response he gives, so he would say "NO!" thereby revealing the truth about the safety of the door!

[@n00blamer]

@@JonCox-hp4fw .. and if you stand in front of truth door with life behind it, he would say YES.. so how you know which door you stand in front of? You need to be certain that the answer has a lie so that it can be cancelled out, only way is to format the question in a way that both doors contribute. "what would the other guard say about this door", then either can be lying and you know answer will be a lie. THAT IS THE ONLY WAY. It's boolean logical statement you learn these in comp-sci 101.

[@JonCox-hp4fw]

@@n00blamer It's not about the door, it's about the guy! If you ask him "If I were to ask you "Is this door safe?" would you say yes?" If he's a liar, he will lie about what answer he would give you! If he's a truth teller, he would tell the truth about which answer he would give you! If the door is death, either one would answer, "No, I would not tell you that this door is safe!" The Liar is lying when he says he would tell you No, but he still reveals the truth!

[@n00blamer]

@@JonCox-hp4fw Death+Liar=NO (you survive), Death+Truth=NO (you survive), Safe+Liar=YES (you die), Safe+Truth=YES (you die) The problem with your logic is that if you're at death door you survive by your logic, but if you are at safe door you die by your logic. You cannot know which door is which, even if you short-circuit the answer. Now you need to know if the door is safe to know which answer to choose, but that's the puzzle: you DO NOT know which door is safe. or which guarding is a liar that's the problem we're solving here. The only solution that works is to know that the answer contains a lie. Your logic gives 50% probability to die, my logic gives 100% probability of survival.

[@OutBoXeR007]

You ask 1 guard an absolute fact like: Am I a human? Case 1: Honest Guard : Yes Now i know that this is the honest guard, then the other must tell a lie Go to the other guard, and ask “Will I die if i go behind this door?” Liar Guard will answer yes or no. Make your decision on the opposite of his answer. Case 2: Liar Guard: No Now, i know that this is the liar guard. Go to the other guard, ask Will if die if i go behind this door? He will tell the truth so do as he says. I followed the rule of asking only 1 question to both the guards each

[@davecorry7723]

_"You can ask _*_one_*_ of them only, _*_one_*_ question."_

[@JZsBFF]

You're dead because you didn't read the instructions.

[@kvasir8931]

The rule is one question only. Not one question each

[@rambido]

For either one, the question is this: "If I were to ask the other door which way to go, what would it say?" And then you go the opposite way. Voila!

[@ganeshjaggineni4097]

NICE SUPER EXCELLENT MOTIVATED

[@Kyzen_Wrell]

But isn’t the only way they could admit that there’s one truth teller and one liar false? Because if the liar is saying “the one of us would speak only lies” that would be telling the truth. The only way they could both make that statement is if they were BOTH lying.

[@TheJM5]

How many fingers am I holding up if one says the right number than its the truth but if the other says the wrong number then he lies

[@123Mathzak]

But what if the truth teller is guarding the death door?

[@infinitevoid227]

That’s the catch, you only get the one question. After you figure out who the liar is, you are out of questions and will never know which door is safe.

[@TheJM5]

Well can’t you ask the other one the question

[@infinitevoid227]

@@TheJM5 nope only one question for one guard. It’d be too easy otherwise

[@TheJM5]

@@infinitevoid227 that’s stupid then how do I know who’s lying

[@Buffbuffrules]

How do we even know which guard is the liar and which one is the truthful one? Because that takes 1 question to figure out and then we need another question to ask the truthful guard where the safe door is.

[@Sarvente---]

Me dropping my weapon infront of the two guard then asking : did i drop my weapon? one of the guard: yes /the other one : no i see this as a win i go to the truthful door

[@d.godummyy]

“What color are the walls of this room?” If answered correctly I’d ask the other guard if their door is safe if the answer is yes, I know they’re lying.

[@BrainFoodforLife]

You’re going the right direction but you have to ask both the same question in this iteration.

[@michaelboykin9881]

Is your door safe

[@cakedo9810]

If you were the other knight in the room, which would he say is the correct door? Then go in the opposite door.