Can you solve the birthday cake riddle? - Marie Brodsky

Practice more problem-solving at brilliant.org/...
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Your friend’s birthday is tomorrow, and he’s turning… well… you’ve forgotten. A ginormous cake has been prepared and your job is to sculpt his age as the chocolate centerpiece. The birthday boy is a giant, and you’re afraid that if your forgetfulness becomes known, you’ll become part of the feast. Can you figure out your friend’s age before the party? Marie Brodsky shows how.
Lesson by Marie Brodsky, directed by Igor Coric, Artrake Studio.
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[@TEDEd]

Visit brilliant.org/TedEd to check out Brilliant’s 60+ courses in math, logic, science, and computer science. They feature storytelling, code-writing, interactive challenges, and plenty of puzzles for you to solve. And as an added bonus, the first 833 of you to use that link will receive 20% off the annual premium subscription fee.

[@thatfabana07]

First 🥇

[@curiouslight498]

Woah, Thanks man! I will surely check this out.

[@radiical6883]

O

[@LOL_MANN]

He forgor 💀

[@pinecone2214]

I think I may have a more efficient solution. What if you were to keep traveling until you see a pattern repeat twice, assuming the pattern length is at least 2, then swap the last candle and go back and see if the last candle in the first itteration changed. If you don't see the new change, now travel forward and do the same again assuming the new pattern length's minimum is that of the total length you've seen so far. Assuming you aren't extremely unlucky with coincidental repeating patterns, then you will only travel to 2x the age, then travel back to a total of 3x+1 of the age. If there are repeating patterns, the minimum length will at least double each time, so it shouldn't take too long, and assuming the candles are completely randomly lit or unlit, the chance of the whole length being just all 1s or all 0s or a similarly highly repeating pattern is low, so you won't be back tracking much. Of course, this requires having a good memory or bringing something to write on or something, because it is more complex, and that might be invalid idk.

[@samcarpenter7104]

The real riddle here is why I keep hanging out with giants who can and will eat me for minor things.

[@arqamshakeel1152]

Because that giant is the owner of amazon and you work for amazon

[@samcarpenter7104]

@@arqamshakeel1152 I need a new job.

[@HuyHoang-ex6pc]

Wow congrats on getting a heart by TedEd

[@quinlynnnelson5030]

It's wild reading this comment before the video has started

[@InazumaRailgun]

because anything else would be too boring

[@joaobello7179]

I love when they pause the riddle to show you the rules, rule number 5 says not to take your clothes off, because is unsanitary and basically tells everyone off because that would probably be an option 😂😂😂

[@AlphaPizzadog]

Bring an extra set of clothes and put them in the cake as markers

[@avic6069]

@@AlphaPizzadog but you have nothing with you

[@vloggerbonakid6178]

@@avic6069 And that's kind of unsanitary for a giant's birthday cake...

[@cozyflurry]

Yea well im not sure the demon of reason will be so kind to follow that one

[@OmikronTitan]

....then the Giant proceeds to blow all over the cake rendering the cake just as unsanitary... if the Giant is sharing of course.

[@OzziePerez1988]

I would just ask the baker since he's the one that installed on the candles 😂

[@dankauthor3364]

I like the use of the word installed

[@JonahWho]

big brain

[@marshmallowdapatria3207]

actually ,the baker will tell the others that you don't know the age and you'll be the dinner

[@ggz21]

Why not be the baker instead, so that you'd know from the giant directly?

[@stephn2351]

👏👏👏

[@teamcyeborg]

Honestly immediate brute-force strategy was to go through and turn off every candle that you come across until you stop coming across lit ones. Pick a random spot and light it; Now go loop around and count the candles until you see a lit one. Turn it off (and/or turn on the two around it, or some other pattern to mark it off) and circle back around the same number of candles. If it changed, you've got his age.

[@lifeartandall3323]

The problem with that i guess is that the giant may be really old, such as 1,000, and you may have not turned off all the candles

[@infinitive995]

@@lifeartandall3323 better than looping the whole candles 21 times as in solution!

[@malickkingofficial3787]

This is what I was thinking

[@awesomenova09]

Exactly

[@realdelana]

That wouldn't work I had the same idea but realised it wouldn't work (all the time, it might work in very short loops), if you you didn't mark any start state and just proceeded to try and turn them all off you might get confused as: 1. Inside the cake you have no idea where you are and how far you have gone since they all look identical ( you wouldn't be sure to sure where to stop since a lot of candles might already be off) 2. Thus you might not end up turning off the candles. 3. If that is the case and you did not turn off all the candles🕯️ and you proceeded to turn one on and started counting till you encountered the lit candle. You could potentially run into error as again you might have not turned off all candles and when you encounter a lit candle, it might not truely be the one you lit ultimately leading you to count the wrong number of candles.

[@clayel1]

Rule 5. “…No removing your clothing either. That’s unsanitary. This is food, people.” damn, they knew what we were gonna think of

[@EmilyRose-op1gd]

it's actually rule 5, but is still very funny.

[@nikhilsharma-jx7zw]

They also knew that if we know the length of the loop we could just count our steps so we know we are at the start again

[@noodleexpanding3407]

Gotta prioritize hygiene over your own life

[@cipher3966]

He kept clothes on and walked all through it. I don't know if shoes on or off are less sanitary

[@adarshmohapatra5058]

Bruh, now that I think about it, the clothing solution should work. As long as you pick up your clothes after removing them & completing a loop. And Ted-Ed shouldn't talk about how unsanitary it is. The giant was gonna eat the cake with me in it if I took too long XD

[@sarahcunha7607]

plot twist: The giant baker guessed the giant's age and didn't put the right amount of candles on the cake

[@HopeRock425]

Well, at least it's consistent with the baker, because having 12 as the number and the amount of candles is better than having 30 as the number (whether or not it's right) and 12 as the candles.

[@pinecone2214]

@@HopeRock425 the giant isn't simply gonna eat another giant. However they will maybe eat a tiny little ant sized thing with ease.

[@HopeRock425]

@@pinecone2214 I was talking about the cake?

[@redluna8865]

@@HopeRock425 i assume what he meant was: If both the Baker & the main hero made mistake in the Giant’s age, he won’t eat the Baker because the Baker is also a giant. But the main hero can be easily put at fault & the comment was replying to Sarah’s

[@hairje1340]

@@redluna8865 the baker is not a giant hes only a bit taller then the character you can see this at 0:43

[@TakeruTakashi]

I think that the morale is clear enough: dont make chocolate ornaments for someone who could eat you for not remembering its age

[@cozyflurry]

Yup

[@dannyluo2077]

I totally agree.

[@Inkyminkyzizwoz]

*moral

[@marsh2melody]

agreed

[@joseleonido3479]

True, a friend of mine got his cousin eaten by a troll that was eight years old.

[@s-b9ifjry7732]

Answers I think should be possible: 1. You should have some sense of where you started, based on the path you took to enter the cake’s interior. Start counting from there until you reach that starting point again. 2. Ask the baker if he/she put enough candles on the cake, keep asking until they unknowingly give away the age. 3. Verify you have green eyes, then leave the giant’s house.

[@aquamarie3117]

"Are you sure there are enough candles on the cake?" "Ozo"

[@stapoldypropagandaaccount]

get in a line alongside the giants and baker and have aliens quiz you on your hat colours

[@catshal1067]

Man ever since that island riddle with the dictator dude, everyone’s talking about green eyes.

[@evinnie6816]

tell the giant that at least one of the bakers has green eyes

[@3amjeed463]

Or you can just turn them all off and then turn every one on and count

[@kaylenvee8150]

Can you imagine if the giant woke up in the middle of the night just to see the candles flickering on and off on their own? You'd never have to worry for time because he wouldn't want to eat that cake anymore.

[@aromi4578]

😂😂😂 lol

[@jaromtoy9163]

I’m a little confused - what’s preventing us from walking around the cake, turning off all the candles until we go for a while without lit candles (supposing he’s timeless and we have no way of being sure of his age), then lighting one and counting the candles all the way around until you get back to the start? Aka, turn all the candles off then count them starting from one candle that you turn on?

[@watermelon.4214]

That's exactly what I thought-

[@0mr_x055]

Because you will never know if those 100 or so unlit candles you passed are off because you turned them off or if it's just a very long phase of randomly unlit candles.

[@thatnike2604]

That's what I thought at first. But when you have no idea how many candles there are, you can't ever be sure that all candles are off. So after you light one up, you could stumble into another lit candle and get the wrong number

[@watermelon.4214]

@@thatnike2604 That makes sense. Thanks!

[@UniHorned]

You walk around turning off any lit candles. If it has been 200 candles since the last lit candle, it means they are all turned off. Turn the one you're at on, and walk around until you reach the same one again, counting the candles as you go, and get the right answer.

[@glo_bin]

The giant waking up after a nightmare and seeing the candles on his cake turn themselves on and off 👁️👄👁️

[@Sapphire-44]

That would be terrifying, especially for a 12 year old. 😂

[@grethelguerra9880]

😂

[@thevofamily7]

Lol

[@marsh2melody]

Lmao

[@gmdFrame]

Too specific. Not funny that way.

[@kaienshiori]

I like how at 4:26 there's objects from other riddles getting blown away with us like the elemental crystals (Fire Crystal riddle), the fabergé egg (Egg Drop riddle), and the gold and silver Tri-source hexagons as well as the gems (Dongle's Difficult Dilemma)

[@teckyuanwang6861]

The riddleverse of TED

[@note5819]

It's slowly becoming its own cinematic universe, and I absolutely love it. The Fabergé eggs (with exact same designs) have made quite a few cameos in other riddles too!

[@thegamergirl6164]

also th earth crystal!

[@kingwolf3044]

I guess I wasn’t the first to notice that. And I thought I named it the riddleverse. Great minds think alike I suppose.

[@DeathnoteBB]

@@note5819I think they had a cameo in the Fire Crystal riddle! They were on top of the containments

[@terabyte3275]

My idea was turning off all candles and checking periodically outside if any candles are casting light. Then going one direction and counting while turning them all on. The first one I see on means I've made a loop

[@acherem13]

Much easier and effective.

[@Klick404]

Wouldn't that take a really long time?

[@Zunree1869]

Bruh same XD, just turn them off then on again.

[@demonflamerslayer252]

That's exactly what i thought

[@hyperfiz0980]

That's what I thought

[@ChaunceyBeggs]

Wouldn't it be more efficient to use prime numbers for your initial guesses? That way you don't need to worry about factors as possibilities. Also, by turning on all candles from the beginning, you can quickly determine if the actual amount is less than your guess (you run into an unlit candle earlier than expected while backtracking) or greater.

[@theothers2744]

Oh, just ask the baker how many candles did he put. If you're afraid of being found out that you didn't remember the age, ask a tricky question to let him spill how many candles are there (or the age).

[@madlad255]

True, I was thinking the same. Saying something like 'Wow, they grow up fast, don't they?' and then subtly pushing the baker to spill the age, should be enough, I think.

[@enneh07]

Tell the baker that you have green eyes and he will tell you the giant's age.

[@daforkgaming3320]

Or have an excuse. Ask him how many candles did he put because you want to make sure he didn’t forget the giants age.

[@CTBOYSTB4L]

@@daforkgaming3320 easy W

[@gregheffley5745]

@@enneh07 Nate, that joke is stale.

[@dinohall2595]

1:26 "No removing your clothing either. That's unsanitary. This is food, people." Best criterion for a riddle ever.

[@-nightlyfireflies-9561]

Ted Ed just in a silly goofy mood

[@NeerajaRaj-fq3mh]

Yes...

[@echojr.801]

Solving one of these Ted-Ed riddles on my own is on my bucket list

[@EnriqueLaberintico]

I've done five of them, but that's less than 1/13 anyways.

[@dannyluo2077]

I sometimes solved some riddles by myself.

[@andrewsteifer520]

Should you count solving one if your solution is logical, reasonable, and works, but isn't THEIR solution??

[@dannyluo2077]

@@andrewsteifer520 I’d say yes.

[@lilmarionscorner]

1:25 Rule 5 reads: "You are carrying nothing with you, and any marks you make will dissapear. No removing your clothing either. That's unsanitary. This is food, people."

[@rinabegum-xh3wq]

Oh my goodness they new nobody reads that stuff

[@INTstincts]

Alternate solution which feels like cheating, but is never called out as being illegal by the rules: Walk around and turn every candle you see off. After some time, exit the cake and see if the room is dark. If not, enter the cake again and keep turning off candles, checking again periodically. If it is, you have turned off every candle, and can re-enter the cake and turn one candle on, then walk the loop until you reach your lit candle. This gives you a definite state you can check for without having to backtrack or make too many additional loops

[@JJisjusttiredoflife]

Genius 💯

[@feliksporeba5851]

​@@tamirasekhar16 No. You could never be sure you turned all the candles off this way

[@kiko_akabane8820]

@@feliksporeba5851 Yea u can. Its a dark room i think u would spot a lit candle

[@giovanniwild7535]

No, this might not work. Assume if the candles were too dim to determine if all the candles are off.

[@amateraceon5202]

My favorite about this is the stipulation saying, “No remove your clothing, either. That’s unsanitary. This is food, people.”

[@shinyagumon7015]

That's the second time that a TedEd riddle contained the threat of being eaten by a Giant. I think the only thing we're learning here is too be distrustful of Giants. Also the bigger question is how can the Giant blow out electric candles?

[@ScorpionClaws789]

The lighting mechanism could just be setting a spark to make the candle burn

[@parikshitbende6168]

That is a big twist

[@TahmidurRahman365]

it's a giant they blow out and up everything

[@Inkyminkyzizwoz]

*to be

[@archivushka]

I I had a quarter for any time TedEd riddle contained the threat of being eaten by a Giant I would have only 2 quarters That's not a lot But it's strange that it happened twice

[@samwhite4284]

I love how comically tenuous the set-ups for these riddles are. I’m really not complaining.

[@stankorzilius]

Nice riddle, with an elegant optimization to the "try every distance"-method. I had a different optimization which I believe will work well in many cases too. First, turn on your reference candle. Then, go into one direction to the first lit candle and turn it off (let's say this is the n'th candle). Go back the same number of n candles and check the reference candle. If it's off, you have the solution. If it's still on, don't go into the same direction to check the next lit candle. Instead, go into the other direction to: - the first lit candle; - at least (n+1) candles away; - with at least n unlit candles before it. On the way, you turn off all candles you pass. Once you've found this candle (let's say it's the m'th candle), turn it off and trace back the same number of m candles again. If it's off, you have the solution. If not, you go into the first direction again. However, because you turned off the n'th candle in the first direction earlier and only just turned of the m'th candle in the second direction, these can't be the same candles. Therefore, you'll look for the first lit candle, at least (n+m+1) candles away, with at least m unlit candles before it. This process repeats until you hit the reference candle. The avantage of going into two directions is that the candles that were previously furthest away are suddenly very close. And by turning off the candles on your way you quickly increase the number of unlit candles surrounding the reference candle. This will make it easier to identify it because you can dismiss many other lit candles which you would normally check too. The solution given in the video is certainly less complex, but my approach is very efficient (too). In the example case of 99 candles, I computed that in the worst-case scenario, you only need to visit 464 candles (instead of the 559 candles in the video).

[@luce5629]

Ted ed: here's a riddle * proceeds to not have a single riddle, instead gives you a series of bad logic puzzle that aren't analogous to any real world scenarios and can be solved with basic communication skills*

[@Jgaldragon]

You could also ask the giant or any tall guest to lift you up to get a better view of the candles. You can tell them you wanted to see how big of a centerpiece you could make with the space available.

[@fairy_queen85]

Hey, that's bloody genius!

[@zachshows2597]

Wow I guess basic problems require basic solutions

[@giovanniwild7535]

May work, but very risky.

[@schuhsuppe7228]

As a person who has to deal with memory loss issues this was a very easy riddle i must say :)

[@oferzilberman5049]

When he said that you can see if the candles are on or off, my mind IMMEDIATELY jumped back to that numberphile video about the Busy Beaver function. It's honestly amazing I think you could just run a trip, turn off all the candles, then turn on a candle every certain number of candles, starting with one. It might work a bit faster.

[@benjaminlee985]

How do you know when you've turned off all the candles, though? Even if you walk past 20 unlit candles, maybe the 21st is still lit.

[@MildlySleepy]

Imagine being the giant and waking up in the middle of the night and see your cake flashing candles

[@The_MeteoriteGamer]

'You forgotten' What a great friend you are 'If your forgetfullness becomes known, you'll become part of the feast' What a greater friend you have

[@twilightbts7058]

The intro and the animation are inevitable and never cease to draw my attention towards the video! I love it !

[@ihavenodogs]

I can’t help but agree

[@wilburn5881]

I've seen a lot of people suggesting turning off all the candles and then counting them by switching them on, with the problem being that you can never know you've turned them all off, as the giant could be even 1000 years old. However in a realistic scenario this ~ *would* ~ work; if we have seen the cake, and it's not too big, we won't have to walk for miles to know that we've switched off all candles after a certain amount of time (same if it's bigger, calculate roughly the time you will walk depending on the size). The thing with this riddle is that for some reason you are not allowed to know any clue based on size and proportions of the very observable cake that you can clearly see.

[@FrostedCreations]

There's a giant, you can't go off of intuition. There's nothing saying it's not a magical cake that seems smaller than it actually is.

[@wilburn5881]

@@FrostedCreations There's nothing saying it is either. You don't go solving problems based on what's not said, but on what has been said.

[@adumba3709]

@@hermannbarbato The rules only state that his age is at least 2, they only said "between 2 and 200" in the beginning for dramatic effect , which is honestly kinda misleading, hence why a lot of people in the comments assume that he's 200 years old at most

[@dimlighty]

Can't you do it this way? 1. Keep turning all candles off as you pass. 2. There will be once at least that you complete the loop and find all the candles on your way forward off. 3. You go for checking many other candles ahead, say 1000, to make sure that all are turned off. If you find all 1000 candles turned off, that means you've probably turned off all candles in the tunnel. Even if the giant's age is 10000 or something, we know that it can't be that 1000 candles in a row would be off as it's very less of a probability for candles lit on and off in a random fashion to be this way. 4. Choose any candle and light it on, keep counting till you reach the lit up candle and you've done counting it.

[@jaromtoy9163]

It’s a misleading riddle. I didn’t rationally think of any way other than this, and the answer seems to support the notion that there was an implied age range. A bit frustrating, but TedEd’s riddles tend to be more of math and logic puzzles, so I guess I can’t complain for getting what I get.

[@LARKXHIN]

I thought this was going to be like an ancient riddle, but it just got more surreal as it went on.

[@respectableaf9061]

And me using logic: Just call the baker. He would know how many candles he put on the cake.

[@sy-ep6dv]

How amusing... This got recommended to me today, today is my birthday.

[@egal1780]

0:25 what a nice friend...

[@tylerwinterton7535]

I'm so happy this actually landed directly on my birthday.

[@parikshitbende6168]

Happy Birthday 🎂🥳

[@nimatamang80]

We're lucky isn't it 👀

[@dannyluo2077]

Happy Birthday.

[@adwanbwah2266]

Same here! Happy birthday!

[@user-uq4xj7uy2y]

Happy birthday

[@mcipher5086]

Easier solution: You can’t leave marks on the cake but you can leave marks on the candle, grab a piece of cake and draw with it a distinct letter or symbol on the surface of the candle, now just count the candles and no matter their state, you’ll always arrive to your marked candle, thus doing only one loop.

[@gregheffley5745]

That's perfect!

[@anshumanagrawal346]

The riddle assumes you can't make any marks or know in any way if you've been at some place before except by the state of the candles, realistically there's obviously lots of ways to make small marks

[@isalima5101]

🎂👄🎂🎊🎊👏🏼👏🏼😃😀😚🙏😍

[@thepoobandit2850]

@@surgeling2 it’s not a real cake bud it’s a riddle

[@deleted-something]

Ye

[@JioLLLL]

Oh my goodness! What a coincidence (or maybe it was intentional)! I'm binging these videos and I saw this comment from 3 years ago: "Why are all these riddles always set in deadly gruesome situations. Give me a riddle about serving cake to children at a birthday party for once." -saakmalo You really came through for her 😂 I hope she sees this video!

[@cindyyeo6161]

still a deadly situation, the giant could eat you for not knowing his age 😂😂

[@stuffes3495]

Me who’s gonna ask somebody his age instead of running a marathon in a cake

[@bivcbmtgstgtssscqcrddgtrsm2257]

That wasn't a particularly difficult riddle, but it definitely had an interesting solution.

[@tanimation7289]

Still as long as it made you think the riddle is a good one.

[@bivcbmtgstgtssscqcrddgtrsm2257]

@@tanimation7289 It most certainly did.

[@danielyuan9862]

It was a good riddle, just poorly explained. It never said anything about efficiency in the problem, and yet that was the core of the puzzle.

[@bivcbmtgstgtssscqcrddgtrsm2257]

@@danielyuan9862 So?

[@bivcbmtgstgtssscqcrddgtrsm2257]

@Lucas My thoughts exactly.

[@the_superdiscogirl]

I love these riddles! More please? They are so challenging and fun!

[@Stellaiseditingandgetsnosleep]

Friend: "are you able to come to my birthday party?" Me: "No" *The End*

[@tera_hz7125]

Then you will be the dinner

[@isalima5101]

Jdnfhfkdorjdk Djdmuddmp Urmegej😍😚🎊😃🎂👏🏼🎁🎊🎈😀👄😁🎉🎂👏😁🎊😃🎉

[@minhtrinhthe897]

I would walk around and turn off all the candles and then start turing them on one by one😂😂😂 TOO EASY CHUMP!!!

[@theydrewa31]

step 1: confirm you have green eyes step 2: politely ask the giant his age

[@DarkSorcerer]

This riddle has a creative solution, and I still can’t solve it

[@Stratelier]

That's because the solution is actually the _strategy_ you would use to confirm the giant's age, not the actual number itself.

[@ChristieMeg]

I love the fact that this was published the day before my birthday 😂

[@nimatamang80]

Me too. 😌 But it feels kinda weird in a good way

[@DircyaT.Rubino]

Happy Early Birthday!

[@ChristieMeg]

@@DircyaT.Rubino thank you!

[@OliverTheAmpersandCat]

Assuming that this cake is a perfect (or near-perfect) circle, and the candles are spaced evenly, you could measure the angle of one candle to another, and calculate how many more candles you would need to finish the circle. Or, in a like fashion, (again, assuming that the candles are spaced at equal intervals) you could measure the distance between each candle, and that would tell you how many candles you would need to complete the circle.

[@nyanSynxPHOENIX]

I thought of that too. Before even beginning to count the candles, you could make a pretty decent estimated guess at how many candles would fit around the cake at equal intervals. Obviously we have seen the cake from the outside, so it should be easy enough to make a guess between 10 and 2000, lmao. Actually measuring out the angle though would be pretty hard since you don't have any tools with you.

[@OliverTheAmpersandCat]

@@bones-f1i I don’t go anywhere without my art-bag. My art bag has multiple rulers and protractors that I would be set.

[@Tii52]

I would leave my jacket behind and walk so much until i stumble into my jacket.

[@JonahWho]

i swear to god, i watch these once and it goes over my head, but then a few years later i go back and i'm like OHHHH I GET THE SOLUTION NOW

[@drmujtabashaikh8]

We can all agree that Ted Ed never fails to entertain us

[@radiical6883]

Yes

[@parikshitbende6168]

Do you to confuse us ?

[@sz5718]

factual statement right there

[@filipfilip1507]

Bot

[@pinecone2214]

I think I may have a more efficient solution. What if you were to keep traveling until you see a pattern repeat twice, assuming the pattern length is at least 2, then swap the last candle and go back and see if the last candle in the first itteration changed. If you don't see the new change, now travel forward and do the same again assuming the new pattern length's minimum is that of the total length you've seen so far. Assuming you aren't extremely unlucky with coincidental repeating patterns, then you will only travel to 2x the age, then travel back to a total of 3x+1 of the age. If there are repeating patterns, the minimum length will at least double each time, so it shouldn't take too long, and assuming the candles are completely randomly lit or unlit, the chance of the whole length being just all 1s or all 0s or a similarly highly repeating pattern is low, so you won't be back tracking much. Of course, this requires having a good memory or bringing something to write on or something, because it is more complex, and that might be invalid idk.

[@Stratelier]

Say you brought a notebook with you and you can use it to take notes -- but you have to take it with you because if you leave it behind you will never find it again.

[@angelerror4086]

I think most people would actually go for ted ed solution lol, this requires considerable amount of brain power, and the videos' solution mostly only contained counting

[@ShortFilmVD]

I suspect this is a more optimal solution for large number of candles 🕯 a similar approach would be to start at a lit candle, turn off all candles as you pass them (bar the first one) walking in one direction unti you reach a lit candle followed by a sufficient run of unlit candles. Then toggle the last lit candle and walk back to the start and assert the first candle is off. If it's not, it wasn't the first candle. The greater the run of unlit candles chosen as the threshold for turning around the more likely you're at the start. Again, if the candle runs get very large this could become slow so maybe consider increasing the threshold complexity at every failed attempt

[@scottclowe]

This is the best solution. The baker has seemingly designed the cake to have some kind of pretty design of lit and unlit candles, and this solution doesn't ruin their design by lighting or extinguishing all the candles while you count them! If you go round turning all the candles on, how are you going to remember the original configuration to reset the cake?

[@scottclowe]

Actually, this solution is very efficient if the candle configuration has high entropy. If it is ordered (e.g. on/off/on/off...) or incredibly sparse (e.g. off/off/off/off/off x1000) then you'll be doubling back on yourself to check very often, in the worst case every other candle.

[@hourofberries]

And then you get eaten, because as it turns out, the giant is turning 120. They just couldn’t fit that many candles on the cake.

[@gregheffley5745]

But it says the giant is your FRIEND. Why would he want to eat you?

[@hourofberries]

@@gregheffley5745 i’d eat my friends if it was socially acceptable and they forgot my birthday

[@gregheffley5745]

@@hourofberries But when is it "socially acceptable" to eat your friends?

[@hourofberries]

@@gregheffley5745 in a world where I’m a giant apparently

[@gregheffley5745]

@@hourofberries But still, the giant probably understands your forgetfulness.

[@adamblessing8528]

The twist: all the TED riddle giants are incredibly kind and all of these workers just have horribly unrealistic anxiety.

[@Solitarius69]

wow this is the first riddle i ever solved, thanks for making riddles keep it up

[@AKS-zl6be]

"How old would you be if you didn't know how old you are?" I will check my adoption files instead of thinking about it. 🙂

[@daforkgaming3320]

I think another way to do this with the first method fast is to use multiple candles. Let’s say you keep 2 candles next to each other on, and you count all the candles until you find another 2 candles next to each other, you can turn those off and track back your steps and if they’re still off, that means you did it. This is like the first but it’s 2 candles. So for how many candles we saw are lit, there are probably be less times that 2 are lit in a row. You can also do this with 3-4 or maybe more candles to make it faster. You can only see one at a time but you can count the number of times you see a candle on/off

[@blakechow8294]

I love the new trend of adding Easter eggs from the old riddles to the new riddles like the eggs from the heist riddle, gems from the auction riddle and the crystals from the elements riddle are at 4:26

[@Imamotherfreakingavocado]

My solution is just, go around and make all of them lit, and then after every candle is lit, start turning them off and count as you're turning them off

[@jasonfakename4851]

Step 1: go around the cake and turn every light off. Feel free to go around as much as you like. Step 2: when you feel like every light is off, turn one on. Step 3: go around one more time, and count every light. Step 4: when you get back to the light that’s on, you know you made one full rotation. This means that you counted all of the candles.

[@gabrielg2395]

This was my solution too.

[@Brudovo3434]

Exactly super easy, and effective

[@Quackleb]

How do you 'feel' like every like light is off? Say the giant is 1000, if you go past 327 candles, turning each one off, and 'feel' that every light is off and turn one on, then when you continue, looking for a lit candle, you might find one only 200 candles later, at position 527. You would assume that is your starting candle and think that the giant was 200, then you'd die

[@ianslater9566]

@@Quackleb you could turn the first candle on, and then keep going until you don’t find any more lit candles. Then backtrack the amount of candles you went, and if there are more candles then you saw, the candle will still be lit. After that, go even farther next time and repeat. Might take longer then the solution in the video, but still works

[@NumbToons]

@@ianslater9566 You said "and then keep going until you don’t find any more lit candles".How would you know there are no more lit candles?

[@totalme302]

I love how Ted ed has to exclusively tell us about some basic manners.

[@zedricktecson]

I would just ask one of the party goers to save myself the hassle 😂😂😂

[@dirantosdelgado4749]

My solution without having looked at the answer: Choose a random candle and turn it on (or it is already on). from there go to the next turned on candle and count the candles that lay on the way. This way you can trace back your first candle. Now turn off the candle and retrace the steps. If your original candle is also off, you know you went in a circle and know the number of candles because you counted along. Otherwise, repeat the steps i.e. go to the next candle that is turned on and so on...

[@5idi]

It's better than the proposed one

[@notAD13]

Well, your method is quite unreliable. Suppose using your method, if we find out that there are 20 candles, then it can't be exactly the answer we need. It can also be that the actual number of candles is 2 and we are just turning the same two candles on and off thinking they're 20 different candles and we won't even know if we are doing so as we are in a loop. The number of candle can also be 4 or 5..and all the factors of 20(as mentioned in the video). If we find out that the number of candles is not a prime number, then there is a possibility that the factors of the number can also be the number of candles.

[@dirantosdelgado4749]

@@notAD13 Let's assume that there are only 2 candles. You choose a random candle and turn it on. There are now two possibilities, either the next candle is on or off. If it is on, then you turn it off, go back to your selected candle and see that it is still on. If the next candle is off, then the next lit candle is your selected candle. You turn it off, go back (2) steps and see that now your selected candle is off and you know that there are only two candles. So why would you ever get to 20? You know the answer as soon as your selected candle is off. Btw my method is the first method from the video ;)

[@notAD13]

@@dirantosdelgado4749 Well see the video. They say exactly the same thing I said after they showed your method of solving the riddle.

[@notAD13]

@@dirantosdelgado4749 And also I never got to 20. I never started off with 2. I just assumed that using your method, we found out there are 20 candles. And here comes more possibilties. There is a possibilty that we just turned on or whatsoever only 2 candles assuming we turned on 20 candles and we won't know this because we are in a loop. The candles are randomly turned off and on so we never know if they ARE or ARE not following the same pattern and i know the probability is less but it's still there. So, we can never assume that there are only two candles. And not only two,there is also possibilty that the candles can be 4 or 5 or 10...(factors of 20). Yes we may be able to find out the number of candles using your method if the number of candles are somewhat lesser but if it is more around even 20,30...it would be impossible because time is limited. We only have time till sun rise.

[@ml-dd1dr]

I would go to the baker and say "hey how many candles did you put on the cake? Cause if you got the wrong amount he's gonna eat us all. How many did you put?"

[@medukameguca5071]

Me with every ted ed riddle: No, I can't solve it but this ain't stopping me from watching

[@SoaringFlame]

Great video as always!

[@veryberry39]

I wanna know why candles are randomly on in the first place. Who leaves random candles burning on a birthday cake for a whole night BEFORE serving? XP

[@kavya.mishra]

What about the entrance of the tunnel? We can just go around the cake from outside and check how many entrances the tunnel has and then go in and count the candles using them

[@minhquannguyen6192]

I guess you just "dive in" and the hole will just close itself, just like how no mark is left behind when you try to note something on the inner wall of the cake...

[@DeathnoteBB]

Presumably there’s a single entrance, if you could just count the candles it wouldn’t be an issue

[@BlatchfordAnimations]

You could just ask the giant to lift you up so you can see the top of the cake, using the excuse of figuring out how big to make the center piece

[@neethathomas3175]

I mean the riddle is easy but since it's ted ed i'm having second thoughts

[@neethathomas3175]

also if you cant make marks HOW DID THEY MAKE A TUNNEL WITHOUT IT CAVING IN

[@insumanth]

Walk first time and off all candles. You can take a second round to make sure everything is off. On one candle and count till you reach it. With just 3 round, you can count the age

[@StarryNightGazing]

you have no way of knowing you went round a complete loop.

[@vertyisprobablydead]

Why would random candles be off or on? Either they're all off or all on.

[@alyssiataylor546]

@@vertyisprobablydead It says that in the video

[@dimlighty]

@@StarryNightGazing Can't you do it this way? 1. Keep turning all candles off as you pass. 2. There will be once at least that you complete the loop and find all the candles on your way forward off. 3. You go for checking many other candles ahead, say 100, to make sure that all are turned off. If you find all 100 candles turned off, that means you've probably turned off all candles in the tunnel. Even if the giant's age is 1000 or something, we know that it can't be that 100 candles in a row would be off as it's very less of a probability for candles lit on and off in a random fashion to be this way. 4. Choose any candle and light it on, keep counting till you reach the lit up candle and you've done counting it.

[@StarryNightGazing]

@@dimlighty you said it yourself: *probably*. The 100 candles turned off in a row could simply be random for all you know. You have no way of being 100% sure with your method, but the question is to actually be sure. If you don't backtrack, it's mathematically impossible.

[@blueface9051]

A question that I have about this riddle, that I haven't seen anyone ask yet is, why are any of the candles already on in the first place? The whole point is to go in and turn them all on yourself by sunrise. There's no reason why the strategy of turning 1 candle on and going all the way around the cake until you're greeted with an already lit candle wouldn't work if this were the case. If there are potentially some already on by the time that you get there, it means the baker who placed the candles in the cake had turned some on randomly.

[@Karhuma]

the whole point is to know the giants age

[@ChanwooPark-me1wc]

이런 수수깨끼들을 다룬 영상들을 보면 저는 항상 해답에 놀라는 저를 발견하곤 합니다. 전혀 생각지 못했던 수학적 아이디어들을 사용해 풀리는 문제를 보는 것은 참 흥미진진합니다. 좋은 영상 감사합니다!

[@ayrazee]

If the giant is my best friend I’d just be like well “I don’t know”

[@camwoodstock]

I told the giant that on one of his birthdays, he had green eyes.

[@mikab.4838]

I love Ted Ed riddles! And I actually tried solving this new one because I watched all the other ones without trying to solve them. My answer was to start at one candle, then go back and forth counting one candle to your right, then one candle to your left, then counting the one to the right of the candle on your right, then counting the candle to the left of the first left candle and so on. okay this is confusing to explain.. Maybe that's why it wasn't an answer mentioned

[@DarkSorcerer]

No matter what the riddle is, Ted Ed always has a Math theme to it

[@kimiivlogs]

what if u just walk around and turn on all the candles until everyth is lit, then turn off all the candles while counting them until all are off, then u'll know his age so easily lol

[@francoisdross5557]

and how do you know when all of the candles are lit ?

[@francoisdross5557]

@Cleu but what about if he is older than 200 ? he's a giant after all, maybe they can live very old. The very point of this riddle is to devise a way to know when you can stop counting. They say 200 in the video, but it can be any number (at least 2, since they specify it, you do not know how high it can get).

[@mimivuong1543]

@@francoisdross5557 Until you see that every candle is lit ig?

[@ranran_dv]

thats what I was thinking of lol

[@francoisdross5557]

@Cleu Did you watch the video? It shows a soution with no upper limit.

[@Noukz37]

This the first TEDed riddle that I actually wasn't lost in, and that my solution was correct! Yay!!! 😀

[@mm_k08]

Easy I would just go around and turn all of the candles after that I will just pick one randomly and start turning of and counting each candle after the one I picked, since the candles are arranged in a loop once I see that there is only one lit up left I'll turn it off and I'll know the age!

[@juliayue8463]

Okay first of all, it should be easy to tell when you've reached all candles by simply turning everything on. after a while you'll find that all candles you pass are beginning to become lit: a sign you've made a loop. Once you've reached a certain interval of candles (say, 100), and everything seems to be lit, turn off the candle you're at. Then you count BACKWARDS in the direction you CAME FROM until you reach a closed candle. If the closed candle is

[@tuxedobob2]

Except that the giant might be 500 years old and you just happened across a patch of 100 lit candles.

[@juliayue8463]

@@tuxedobob2 if you read what I wrote, you would know that once you reach a closed candle, you'd shut off the one next to it and run back to see if there were two off. if there were, you've made a loop and now know that giant's age. if there weren't, you go back to where you stopped, turn them on, and continue once again. also, i said "100" as a hypothetical interval you wanted to test; you turn everything on until everything seems lit and that you can guarantee that there are at least 100 candles in a row that are lit. it's so that you won't waste your time running back and forth to check if there are two candles off. you close the candle you're at and begin counting BACKWARDS until you get to the next candle turned off. if you find that 5, or 10, or even 99 candles later you find one turned off, you KNOW the giant's age and can be CERTAIN because you MADE SURE that 100 candles in a row were turned off. If not, then you simply keep checking and rechecking without wasting time to see if you've reached the age.

[@ethanhunt6725]

Oh ma God I love your animation ❤ Theme is fantabulous as usual Kudos, entire team for incessantly entertaining us through your insightful & informative works Love ❤

[@laughingatthesky7]

If I were them, I would just find an object taller than the cake to climb on top of and then count the candles while at the top

[@ghazalalweish6388]

I love those riddles! 🥰🥰

[@NumbToons]

My own solution was very complicated. Create pattern [on,off] [on,on,off,off] [on,on,on,off,off,off] and so on. Needed a lot of back tracking as well to see if pattern in repeating etc. But I think it worked.

[@chipchapchop5808]

why cant you just turn them all off, then turn one on and count how many there are before you get back to your one single lit candle?

[@vincenturquhart1370]

You would need a way to know for sure you have turned them all off, if you keep going clockwise turning off candles and at some point stop coming across lit ones then you could have turned off all the candles or you could be going through a massive series of off candles. the giants age could be huge remember

[@renocool1558]

At some point you would know they are all off, then you could turn one on. I think that is correct strategy

[@vincenturquhart1370]

@@renocool1558 how would you know they are all off? the whole point of the method in the video provides a way to prove you have seen every candle

[@renocool1558]

@vincenturquhart1370 you can assume after seeing 100 candles all off, that they are all off. If turn one one, count tell you see one one, and for confirmation keep going and count again. You'd get confirmation to high degree of certainty

[@vincenturquhart1370]

@@renocool1558 the assumption in these logic puzzles is that we are looking for a 100% proof solution. not a high degree of certanty

[@Hammie72]

why don't you just take off the stealth suit and use that as a marker?

[@netherite9051]

0:11 the look on 'your' face is absolutely horrifying

[@webby_bandit]

First I'd turn off all the candles, turn on one, marking the starting point, and then count from there!

[@ImTheCrew]

This is good information , especially next time it happens to me

[@ScorpionClaws789]

Faster solution - Turn the lights on and off in a pattern (2 on, 2 off), but make your starting point off from this pattern (3 on, 3 off). Count the candles as you go. Once you reach your break in the pattern, check the next set of candles. If they match the pattern, you counted them all. If not, it's a coincidence and you should keep going until you see another example of your starting setup

[@StarryNightGazing]

how can you know it's not a coincidence anyway? to solve the problem, you definitely have to backtrack. otherwise, it's mathematically impossible.

[@iamserious2464]

0:53 You could see him/she wearing boots. Then y didn't the person take off one of their boots🤷🏾

[@Okiahnnus]

Similar to others comments, a far simpler and more efficient approach than those proposed within the video exists. For ease of explanation, this process assumes to some degree that the candles are placed randomly, although this is not necessary to correctly determine the outcome. Rule 1: Continue around the cake in the same direction (unless following step 4) Rule 2: Count the candles during each operation Rule 3: If the outcome encountered is different from that expected (before the current step is complete) return to step 1B. Step1A: Having chosen an initial direction to navigate the cake, turn all candles to one mode of operation, this step is to be considered complete when a consistent group of candles is encountered that are orientated to the current operation. Step 1B: (while keeping track of both the initial count when a grouping is encountered and values extended counts) check by counting an additional 10% into the newly encountered group > adjust count in accordance of findings. Step 2: Proceed to flip candles to the opposite state. This new count should terminate with a value slightly smaller than the first count. Step 3: As a double check to the prior check, now continue turning each switch to their opposite state. needless to say the 3rd and 2nd counts should match. Step 4: And finally check the result by changing the orientation of a single candle and making a final pass around the cake counter to the previous rotation (needless to say while counting)

[@keiabun5245]

I’d just go from the last lit candle and start on the candle after that, turning off every candle that’s lit until I see complete darkness my second loop, then the one candle that’s lit is the answer. To check, I’ll count the candles first then turn off the candle. I’ll go backwards this time, and if I see total darkness, the answer is right!

[@notzack6438]

Lol the transition to talking about Brilliant is well.... brilliant

[@FrostglowASMR]

Wouldn't you know that you had made a full round when you were back at the entrance?

[@StarryNightGazing]

no markings

[@FrostglowASMR]

@@StarryNightGazing So the entrance disappears behind you and you will have to eat you way out when you're done? Otherwise you should be able to find the entrance again.

[@noodleexpanding3407]

This guy asks the real question

[@FrostglowASMR]

@@noodleexpanding3407 Or: I'm not very smart and the only way I can solve these riddles is by breaking them ¯\_(ツ)_/¯

[@RobjectionableContent]

@@FrostglowASMR "So the entrance disappears behind you and you will have to eat you way out when you're done?" Presumably, yeah. Fortunately the exit you make would also disappear, leaving no evidence of your midnight investigations except the candles' states being in a different pattern.

[@kurumi394]

You could just turn on every candle you see, then when you're sure there are no more unlit candles you can start turning them off

[@justinjoseph735]

This is exactly what I thought!

[@thatnike2604]

Well the thing is... you can't ever be sure that all candles are lit. Because it could be any number, you won't know when to stop

[@StarryNightGazing]

and how can you be sure though? lol you make it as it's obvious

[@justinjoseph735]

@@thatnike2604 oh yeah! Darn!

[@justinjoseph735]

@@StarryNightGazing it felt obvious, but its clearly not😂

[@jimmykitty]

First 😊❤

[@Xavier-pt4mp]

Here's my solution(not sure if it's correct, correct me if im wrong, thanks) Unlit any lit candles and count as you go. After all the candles are unlit(let's put an example, 50.), you want to lit 50 candles in a row, and start counting the remaining unlit candles until you reach a lit candle(say, this is 30), you'll get 30+50=80 as your answer.

[@BlackSaiyan24]

2:26 ‘you might have a marathon to run before sunrise, and you definitely don’t want to be in the cake when he starts digging in.’ 1:26 Rule 6 literally says “you may wander through the tunnel as much as you wish.”