How To Solve The TRICKY 10 Coins, 3 Cups Interview Question

[@craigorr9713]

I had a math professor that asked a similar riddle: Q: You have three cups of coffee and twenty sugar cubes. How do you put an odd number of sugar cubes in each cup using all twenty cubes? A: Put one in the first cup, one in the second cup, and 18 in the third. After all, 18 is certainly an odd number of sugar cubes for a cup of coffee.

[@RCmies]

at least that's a bit funny

[@joermnyc]

The only way I can stand the taste of coffee is with 18 sugar cubes. 😉

[@skippytheaustralian9438]

Try again with 42 sugar cubes

[@anoldaccount7264]

@@joermnyc no way,thats too sweet

[@aladdinnosugar8129]

Correct A: Put five in the first cup, five in the second cup, and seven in the third. For the left one sugar cube just eat it. Now, all the cups have odd number sugar cubes

[@Cowinspace]

3 coins in each cup minus my 10% sorting fee.

[@yurenchu]

LOL, smart thinking! Reminds me of Malba Tahan's story about the three sons who had to divide an inheritance of 35 camels. (According to the will, the oldest son should receive 1/2, the middle son should receive 1/3, and the youngest son should receive 1/9.)

[@pooydragon5398]

Adding a ghost camel does the trick ❗

[@KenPaulsenArchitect]

@@yurenchu Reminds me of the farmer with 19 cows with the oldest son to inherit at least 1/2, the middle son to inherit at least 1/4 and the youngest at least 1/5 without dividing a cow..

[@harshitrawat811]

I thought of tge same thing

[@Slimmeyy]

@@KenPaulsenArchitect it's considerably different though because that one is actually easy to solve: 10, 5 and 4. There's no cows to be added or handed out for free like with Malba Tahan's story.

[@darreljones8645]

Here's a related riddle: Two women were drinking coffee at work. Each put an odd number of sugar cubes in her cup. Combined, they took a total of seventeen sugar cubes. How many did each woman take? The answer: The first woman took one cube, which is an odd number. The other took sixteen cubes, which is certainly an odd number to put in one cup of coffee!

[@michaelempeigne3519]

+Darrel Jones That is easy. 1 + 7 + 9

[@darreljones8645]

+Michael Empeigne No, there were two women, not three.

[@chetanphoenix]

+Darrel Jones I love your solution better than this dumb video.

[@daviatu]

+Darrel Jones haha, that was a good laugh! :D

[@harvrathor791]

+Darrel Jones 16 cube ?

[@mcbpete]

If I went to a company that had cups shaped like that I would know it wasn't a good place to work for

[@LP-fr7gj]

Lol

[@scottbilger9294]

You don't remember those old conical Solo-brand cups that you put in a holder?

[@lool8421]

employees cannot place these cups, so they have to hold them, making them want to drink stuff as quickly as possible, so they will go back to work

[@abacusamateur5264]

@@lool8421 Oh, that's actually kind of big brain

[@hunterjoy1871]

I thought it was part of the solution bc the cups can lah on there side and half a coin in 2 cups

[@pvanukoff]

These "think outside the box" riddles are ridiculous. Here's another solution: 3 in the first, 3 in the second, 4 plus an additional 1 from my pocket in the third. There, I placed the 10 coins and each cup contains an odd number of coins. Puzzles are easy to solve if you can cheat.

[@yubjuli]

+Paul Vanukoff Here's another, place 1 coin in each one and take the rest and leave. Win/win.

[@pvanukoff]

+yubjuli Hah, yea, I thought of that, but the question, as worded, does require the 10 coins to be placed into the cups.

[@Hugh.Manatee]

+Paul Vanukoff It doesn't say that you can't take them out after you put them in...

[@malcolmbryant]

+Paul Vanukoff Agree with your solution

[@katzen3314]

I melted one of the cups and turned it into a spork, then put one coin in one cup, nine in the other and threw the crappy spork in the bin.

[@gutz1981]

This is not a "Brain tease" question. This is a "I made the question, so I can screw around with the dynamics and factors of the result in order to make the participant look less intelligent by making a result based on a cheat" quiz.

[@OneWeirdDude]

It's perfectly legitimate, you just have to think outside the (mathematical) box, as it were.

[@sonalidasgupta3562]

@@OneWeirdDude ....which means...everybody can get their own answers 😆 PS: you reminded me of a saying: ....every problem has a solution PROVIDED the word "solution" is suitably defined.....😈

[@OneWeirdDude]

@@sonalidasgupta3562 What's your answer, then?

[@sonalidasgupta3562]

@@OneWeirdDude ☺ believe-it-or-not....but this one time i got the right idea...put-glass-in-glass....usually i am very poor with riddles

[@YaqubAssy]

you are right, man!

[@iwanabana]

one in each cup, I get 7 coins

[@malcolmbryant]

+iwanabana At the outset -- he didn't specify that all coins had to be used, so 3+3+3 would work.

[@nekogod]

+melancholiac The question explicitly states, put TEN coins in the cups. So it is specified.

[@NetAndyCz]

Yeah put 10 remove 7, even numbers in cups ensured as long as you keep 1 in each:)

[@GrndAdmiralThrawn]

Dang, I said “put 5 in one cup, five in the second cup, then put one of those cups in the third cup”, but I was joking.

[@remus-alexandrusimion3439]

I came to the right solution about 3 seconds before they said it. And I, too, was thinking it as a joke...

[@gopackgo4036]

Hindsight bias

[@madhusudanchunletia7459]

Mee too 😂😂😂😂

[@Edos512]

that was my first solution as well

[@tolkienfan1972]

This was my answer. Add three odd numbers gives an odd number, so it's immediately a trick.

[@want-diversecontent3887]

Remove one coin from the first cup, this makes an anti-coin which disintegrates the bottom of the first cup. It is no longer a cup. (Edited in the replies) Only a quarter of a coin was needed, so with an electromagnet I picked up the coin and disintegrated the second cup. I put the remaining eleven coins into the third cup.

[@shivanshsanoria4053]

Lol , this comment needs more likes

[@invenblocker]

Yeah, but now you have eleven coins that you need to dive between the two remaining cups.

[@want-diversecontent3887]

@@invenblocker Ah, but there's still half of the anti-coin left. Not all of it was needed to destroy the first cup. I pick up that other half and put it into the second cup, so now there's only one cup left.

[@Green24152]

@@want-diversecontent3887 Wouldn't that destroy your hand too?

[@want-diversecontent3887]

@@Green24152 Not all of the half was needed, it only took a half because it partially dissolved into the table. And I used an electromagnet.

[@chetanphoenix]

Who said the cups can or cannot fit into one another? This is using a social trick (where cups fit in one another) and not strictly mathematical.

[@malcolmbryant]

+Chetan Bhadrashette Not all cups can physically contain another.

[@SOLAR_WillToWin]

Actually if you look at the picture, the cups could not fit together haha. Especially considering they appear two dimensional!

[@sonalidasgupta3562]

....um...Presh clearly mentions it is a "mathematical impossibility"......THEN ...he talks of "creativity" 😈

[@stephenhousman6975]

@densch123 Usually these tend to test you by asking what you can or can't do with the cups. I would usually say some thing like if I am force to not move the cups around then it is impossible. If I have the possibility to move the cups there are a few ways that this can be done and give an example.

[@scottbilger9294]

I got the answer. Since it was impossible -- a trick question -- the answer had to be a trick as well. It's the Kobayashi Maru Lesson: if the problem is impossible, CHEAT.

[@GretgorPooper]

Ughh, I hate when questions have this kind of trick to answer. I knew a "honest" solution was impossible from the start, which's made obvious by simple arithmetics, but I expected it to end at that, not to have a little "trick" that would never occur to me :\

[@ianyapxw]

+Gretgor LOL haha I can see where you are coming from but these riddles expect you to think out of the box. Once I knew it's arithmetically impossible 10 - (2 x odd numbers) = even number, I knew there had to be an unconventional solution

[@nekogod]

+Gretgor LOL Occured to me almost instantly since traditionally it's impossible so a trick was expected

[@Sorestlor]

+Gretgor LOL My answer would have been you cant add 3 odd numbers and get an even number so uh createa a dimensional rift between two cups. Besides lots of cups dont stack inside eachother.

[@MyPiez]

+ianyapxw That's like saying: What has 3 legs, sounds like a dolphin and also quaks like a duck.... A thing that has 3 legs, sounds like a dolphin and also quaks like a duck.

[@ianyapxw]

+My Piez That's different, because it is possible to put one cup in another (I'm thinking red solo cups) and the cup answer requires someone to think out of the box. The 3 legs, sounds like a dolfin, quacks like a duck is just lame

[@phampton6781]

Top tip: make it more challenging by using Klein bottles instead of cups.How many coins in a Klein bottle? The same as how many outside. Errr....

[@RehanKhan-si1oi]

Comment of the day😂😂😂

[@ValirAmaril]

so if I have a klein bottle, in a way all the coins in the world are in my possession since they're in my bottle?

[@remus-alexandrusimion3439]

@@ValirAmaril Good luck explaining this to any judge, though :D Besides, you can't really have a klein bottle in 3D so it's a mute point...

[@mu-qk2ov]

@@ValirAmaril No, all coins in the universe. So like some alien "coins" (i guess they can be shaped any way, just have the same function) made out of some crazy material that scientists study and later develop, or some coins from an insanely valuable material. Also you're gonna be able to buy things from alien civilizations, so like you can maybe buy some superpowers or a device that is thousands of years more advanced than what we currently have. Its so much more than having all the pennies

[@JonathanGray89]

Screw that. A cup with 4 coins has 3 coins in it by inheritance. 3 is an odd number. lol

[@alakro1356]

+Jonathan Gray - That is the best answer of all. Thank you.

[@nickbarkowski1824]

If this question is asked during an interview, I hope every interviewer has cups that are designed to stack into one another. Three coffee cups won't do it. Dixie cups? Sure. Coffee cups out of a vending machine? Sure. But you cannot use any three cups that happen to be lying around. Anyway, my answer was to simply reach into my pocket for an eleventh coin and toss into any of the three cups. 3, 3 & 5. No one said i couldn't reach into my pocket for more another coin.

[@tomdekler9280]

Honestly I think that's a pretty great answer to an interview question, make a litle sacrifice to solve the issue quickly.

[@phs125]

From my crackingthecryptic odd even sudoku experience, I figured out within 2 seconds that 3 odd numbers always add up to an odd number, so it's an impossible puzzle.

[@DhoklaAboveVadapav]

Man of culture

[@MrChonkers]

9-1-0 proceed to discuss with interviewer the meaning of life, the universe and if 0 is odd. If things get out of hand, use the video method - put the cup with 1 coin in the empty cup.

[@Agnostic080]

+thedarkone123123 xd

[@Deathranger999]

0 is an even number by pretty much all standard definitions of even. Check out Numberphile's video on it.

[@WhovianMinecrafter]

+thedarkone123123 0 is not odd

[@OoleoleoleO]

+WhovianMinecrafter All even numbers have the form: 2n Odd: 2n+1 Yeah, you can't make 0 with 2n+1 Therefor, 0 is even

[@albertoguarnieri5182]

+WhovianMinecrafter I think that's what he was trying to say

[@RB-mm7ce]

Ehhh... I've lost 5 minutes trying to figure out how to solve this problem :P I was even whispering to myslef "No shitty tricks like placing one cup on another, or placing coins od edges of two cups, right ??" GRRR !!!

[@unvergebeneid]

+Radoslaw Brzostek We should have worked together because I quickly proved that there is no partition of 10 that qualifies the criteria but then I went "oh fuck it, so it's some 'find the right way to cheat' solution that I can't be bothered to find." I didn't think of stacking the cups.

[@RB-mm7ce]

Penny Lane Yea, complements perfectly BUT failing on this will make us more aware of tricky possibilities in the future ;)

[@RochesterOliveira]

+Penny Lane exactly what I thought after thing about it a little bit. I'm glad I didn't lose 5 mins like +Radoslaw :)

[@PDionneGosselin]

+Penny Lane Pretty sure it does not even work with any total even number of coins and uneven number of cups. So even partitions of 10, 12, 100, 10000000, with number of cups 3, 5 ,10971. 1 am,after taking an exam lol might not be thinking straight.

[@demonschnauzer1555]

If I got asked this in an interview, I’d just walk out.

[@camerongray7767]

Well firstly, tax takes 10% of coins, so now you have 9. Place 3 in each cup

[@Sekir80]

Haha, imagine this test and your answer when you apply for a job at IRS.

[@SmoochyTea]

It might be a cultural discrepancy, but if I got this question in an interview (on a level of Facebook puzzles for boomers), I would not take the other party seriously at all. Remember, you are not the pawn of some corporate foreplay. You have value and deserve to be taken seriously as a professional. Have a nice day .. =)

[@supercool1312]

hi pressure locker (closed captions lol)

[@HumaraBharatDarshanBR30]

I used to think "Press the locker"🤔😂😂😂😂

[@shamanjitsingh7267]

Lol , Just turned on the captions

[@TheKingBeyondEverything]

His name is under the video also

[@mark91345]

As soon as I saw the question, I realized you had to manipulate the cups themselves, as simply dividing an even number of coins into an odd number of cups cannot work. It is true that one must think out-of-the-box, but an answer equally as valid, if not ridiculous, would be to MELT two of the coins together, so you now have only 9 coins.

[@theonewiththeeyeoftruth884]

I came up with this solution: In 3 separate cups, there is _no way_ to put an _even_ number of coins into 3 cups so that every cup has an odd number of coins. _Three_ odd numbers added together _must_ make an odd number. So this would work: 1. Cup 1: put 1 coin in 2. Cup 2: 6 coins 3. Cup 3: 3 coins 4. Put Cup 1 _part-way inside_ Cup 2 so that the 1 coin in Cup 1 sits below the rim of Cup 2, and therefore the 1 coin in Cup 1 is also in Cup 2 Now: - Cup 1 has 1 coin (sharing that 1 coin with Cup 2) - Cup 2 has 7 coins (sharing 1 coin with Cup 1) - Cup 3 has 3 coins All 10 coins are distributed to the 3 cups, and _each cup_ has an odd number of coins in it.

[@davidjames1684]

Another solution is to just put 3 coins in each cup initially, place the last coin in one cup and then remove it. The instructions didn't say all 10 coins have to remain contained. After you place all 10 coins into the cups, you can do other operations according to the rules since there is no restriction about that.

[@Diaryofaninja]

not sure why people are complaining about 'tricks' mathematically you would see there's no solution so there must be some wordplay involved or some trick involving the objects... immediately came to the conclusion that if you stacked the cups it'd work out

[@jinception01]

My idea before having it revealed: You can't split 10 into 3 odd numbers. 3 odd numbers combined will always be an odd number and 10 is even, so clearly you need to pull some "outside of the box" bs. My idea is to stack two of the cups so one is in the other, then place five into each one. That way, both of the stacked cups contain 5 coins, and the remaining cup also has 5. Edit: eh I was close. Given the condition that coins being in a cup inside a second cup still counts as all the coins being inside the second cup of say I was more or less right

[@svencuyt9629]

I could argue that the cup still doesn't contain an odd number of coins.

[@Erik20766]

When the answer to a problem like this is thinking out of the box, you're not creative if you don't come up with the solution. When the answer isn't thinking out of the box, you're braking the rules, just that the rule you broke was so obvious they didn't say it

[@guiguspi]

To all of you who are complaining or saying the resolution was cheating: This is not a mathematical problem, this is a practical one. If you model it in a mathematical way that doesn't enable you to solve it and get stucked there, then you failed to solve this problem. Deal with it and try to learn from it. Cheers.

[@jacksainthill8974]

You don't need to go through all of the variations 1+1+8, 1+2+7 etc. to show that some trickery is required. Instead, merely note that as soon as precisely two cups are given an odd number of coins each, that's an even number in total, leaving behind only an even number of coins for the third cup (since subtracting an even number from ten must leave an even number), which is contrary to the rules. At least one trick to get around this snag is fairly obvious, but I'll not give it away here.

[@vaibhavsrivastva1253]

Please reveal it now!

[@softwaredeveloper6791]

The convex nature of the second cup generally precludes the English definition of inside to be applied to the first cup. For example, if you had a cup of syrup, and then you placed the cup of syrup into a second cup. Would you truly believe that there was any syrup in the second cup? No, because the syrup was not touching the second cup.

[@jmw8403]

Actually, another solution to this problem is all of the examples you gave initially. If you have a cup with 2 coins in it, then it does contain 1 coin (also). 1 is an odd number and therefore the cup contains an odd number of coins. The questions does not ask for only odd numbers, it simply asks for an odd number to be contained inside of the cup and no matter what number you have > 0, there will always be an odd number inside of the even number and that is all that the question asks for.

[@johnfaustus1]

Boo on Presh for, what is essentially, a trick question. I'll save everyone a click: 1 of the cups HAS to contain an even number of coins, it's just that another cup with coins is placed in it, bringing it's effective total to an odd number.

[@edancoll3250]

Here's my solution (which is just as stupid): Place 5 coins in the left cup and 5 coins in the middle cup. Now tell the right cup it owes 1 coin to the left cup, meaning is has -1 coins.

[@simonenoli4418]

that would make the left cup have 6 ;) my idea was to split a coin with two half valued ones xD

[@jetkirby]

+Timothy Barth try telling a broke cup to pay back that 1 coin it doesn't have, it's never going to happen theoretically the cup on the right has -1 coins, but will never give the coin it owes, so edan coll is correct

[@fortytwo6257]

+Edan Coll My solution was to have negative coins too! Lmao

[@Applest2oApples]

Presh Talwalker certainly had an odd number of strokes while recording this video

[@spockslefteyebrow8327]

I feel like these questions aren't "tricky" so much as they are absolutely uselessly random. Like, it's trying to be smart, but it's a 20-minute long sitcom that NEEDS a beginning, middle, and an end and they don't care if it makes sense or not. Anyone who flaunts this as being "smart" is delusional lol.

[@nbartlett6538]

This answer is clearly just a cheat or a trick. I could just as well argue that the original challenge doesn't say that ALL ten coins must be used, so I just put one to the side.

[@vlastasusak5673]

Interesting. Makes me wonder, if a mouse eats grain, and is then eaten by a snake, has the snake eaten the grain?

[@epiccheesecakexd9213]

I might seem weird, but I think I found an other way of doing this. Take any combination like this: (2n+1)-(2k+1)-(2m). Then place one coin of your own into the even cup You now have the 10 coins in the 3 cups, each cup containing an odd number of coins. The problem does not specify that only the coins given count towards the number of coins in the cup, neither does it mention anything about not using your own stuff. Hopefully I have not missed anything!

[@kerryburns6041]

In the solution, each cup does NOT contain an odd number of coins. Stacking two cups together does not make them one cup.

[@gamiac4777]

You're wrong. One cup has 5 coins, another has 3 and the last one has 5 coints and a cup

[@dylanogden9337]

I put the mouths of two cups together, put three in each cup and balanced the last coin between the two joined mouths. That way the last coin is in the cups but the cups only fully encompass three coins each. It's a way to solve the problem if the cups don't fit inside each other. My solution plays with the definition of "contain", but so does yours so I feel okay about that.

[@gustavo_crivelli]

Better yet if the cups are not transparent, you could shake them and this would become Schrödinger's coin, where the cups contain and do not contain an odd number of coins inside (with let's say, 7 coins inside the 2 cups and 3 in the other one)

[@jasonbourne4865]

I figured out the solution pretty quickly, but was a bit disappointed when it turned out to be the "correct" one. :)

[@katier9725]

Any puzzle can be "solved" if you cheat hard enough.

[@stephenkamenar]

So I thought "this is impossible" is this going to be some trick question garbage where he like puts a cup inside another cup? YUP also why not simply put 1 coin in a cup, put that cup in another cup (both cups have 1 coin), put the other 9 in the 3rd cup

[@Zwijger]

+Stephen Kamenar That is also a completely legit answer, he never said this was the only way to do it.

[@pedrogarcia8706]

That's the 0 1 9 solution. He mentioned it

[@AngieMyst]

I'm pretty sure the cup on the bottom still has 2. Putting one cup into another does not make it a singular frankencup...

[@The_Scouts_Code]

I figured out this solution instantly on seeing the title of the video and watched to see if i was right. The problem is that technically the first cup does not contain the inserted cups contents so i discounted the solution as not really having solved anything.

[@KillerOfU33]

But see, you didn't include that the cups could fit in eachother. That's a crucial detail that, without being mentioned, we psychologically would just assume isn't the case and/or is unimportant. This puzzle is interesting, but how you presented it was unfair.

[@samoparminuta489]

Does 0 count as an even number? If it doesn't, no one said we HAD to put all of the coins in all 3 of the cups. Therefore, we could split them up and put 1 in first, 9 in second, and none in third. You can make other combinations using this method.

[@Jay_76]

I put 3 coins into two of the cups and 4 coins into the third cup. Then I say that the third cup is odd due to having a different number of coins in it. Conversely, the rules don't specifically state that all three cups must contain at least one coin. So, by placing 5 coins into two cups and leaving the third cup with 0 coins there are no cups with an even number because 0 is considered neither odd nor even.

[@vilts]

From now on every time that kind of question comes up we'd need to ask at least 10 additional questions about the rules of the game. Do I have to use all the cups? Do I have to use all the coins? Can I break one container? Can I add/take away coins? What if one cup accidentally broke? Is 0 even or odd number? Can I use imaginary coins? If anything is allowed, then just throw away 2 cups and 1 coin etc. I think these are silly questions and really don't really show how well one will perform in a job position. That's been shown in some studies as well, afaik.

[@gagaoolala9167]

This is just dumb. If someone told me this question I would get out pen and paper, prove that it's not possible, and tell them that they're being dishonest - that's not a good puzzle at all.

[@albingrahn5576]

math nerds in the comments are seething, you love to see it

[@akshin1556]

Take the middle cup and place it on top of the first cup, and that makes them one cup ... Uh, no. Just because you put one cup on top of another does not transform them into a single cup. They are still two separate cups, one of which has an even number of coins in it. I knew from the start that it was mathematically impossible to split 10 up into three odd numbers, because any two odd numbers will add up to an even number, and an even number subtracted from another even number (10) will result in an even number. I was genuinely curious to see how they would make it possible to do it. But putting one cup on top of another ... That is just SILLY. This is not "thinking outside the box." It's just cheating, as many other commentors have said. You could just as easily drop the 10 coins into the three cups randomly, and then take out enough of the coins to make them all odd, because the rules didn't say that you couldn't take the coins out after you put them in.

[@micaelstarfire8639]

This must have been the interview question for Enron. It's not mathematically possible, but let's get creative.

[@timothyball3144]

Right, and that would be the purpose of the question at an interview. It tells them how this person solves problems. Many different ways to do it, but can the person justify their solution?

[@ryanphillips9657]

Stacking the cups appears to the obvious solution. How ever when you look at the diagrams those cups are equal in size and have straight sides. Those particular cups would not fit one inside the other. How ever when you look at the diagrams those cups are equal in size and have straight sides. Those particular cups would not fit one inside the other. The answer to the question is null set.

[@Mariorox1956]

Nine in one cup, one in another, and place the cup with one coin into the empty cup. Don't wanna dirty that third cup if you don't have to, right? You don't know where those coins have been.

[@GM_Neo]

When he did the animation I went from "split one coin in half" to "what if you put one cup inside the other?"

[@ArionKrause]

By that logic you could just smash the 3 cups. All remaining cups (which should now be 0) contain an odd number of coins. And you cash in the 10 coins.

[@noamtashma2859]

indeed

[@cryptexify]

+Arion Roberto Krause But the crushed cups now contain 0 coins, which is an even number.

[@ArionKrause]

+cryptexify Well, crushed cups actually are just broken glass, not cups anymore..

[@LivingChords]

+Arion Roberto Krause So the cups do not contain any coins, which is neither even nor uneven. The problem is fair, you just have to bend the rules.

[@noamtashma2859]

Actually, all cups contain an odd number of coins, although there doesn't exist a cup which has an odd number of coins. The real problem with the solution is that we should have put all the coins inside cups; now all of our coins are outside cups, which is against the terms of the question.

[@unvergebeneid]

Better 10 coins and 3 cups than 2 girls and 1 cup. Sorry, somebody had to make that joke.

[@subbies7881]

I came up with 3 solutions : 1) impossible according to the pigeon hole principal 2) 1, 1, 8 ( since 7 is a subset of 8 and 7 is and odd amount of coins, the last cup contains a set of odd coins, it just so happens it also has subsets of even coins) 3) 1,1,8 but you stack the last 2 cups, so you have 1 ,1 ,9

[@marymaryquitecontrary]

The solution does not, imo, fit the challenge, which states that "each cup" contains an odd number of coins. Stacking two cups does not make them one cup.

[@gamiac4777]

Think about it like this, you have a red bag with 2 pens and a black bag with 5 pens. If you put the red bag inside the black bag, you have 7 pens in the black bag.

[@stevepatching8107]

You still have one cup with an even number of coins. Sticking it on another cup doesn't change the fact.

[@CallahanSF2211]

This assumes one cup will fit in another cup.

[@samarthmehta8732]

A better question would have been, " none of the cups contains an even number of coins", in which case, the answer would have been 5+5+0

[@dannygjk]

A good interview question for companies who are looking for people who are willing to bend rules. That said I did solve it because I quickly realized that a conventional solution was not possible because if you add an odd number of odd numbers you will get an odd number therefore I knew that a trick was necessary to solve it.

[@henrydavis8910]

A more general solution is this: put an odd number of coins (7 or less) in cup A and an odd number in cup B (but less than 10-A), leaving an even number in C. Then place either cup A or cup B into cup C. This allows for 20 possible solutions: (1,1,8), (1,3,6), (1,5,4), (1, 7, 2), (3, 1, 6), (3, 3, 4), (3, 5, 2), (5, 1, 4), (5, 3, 2), and (7, 2, 1), followed by placing cup A into C, or B into C.

[@adamrussell658]

I love the algebraic method you showed. I did it slightly differently. Put an odd number in the first 2 cups. odd + odd = even Whats left has to be even because 10 - even = even So you cant have an odd number for the 3rd cup.

[@jumpman8282]

Here's how I did: If each of the three cups holds an odd number of coins, then the total number of coins is also odd, because ODD + ODD + ODD = EVEN + ODD = ODD, and we can thereby conclude that it is impossible to divide 10 coins into three cups so that each cup holds an odd number of coins.

[@aboudawik7973]

Mathematically impossible Because odd+odd+odd = odd, but 10 is even. But I think there's a trick or something. I think it is like this : Place 5 coins in each of two cups Place a cup inside another.

[@maxlepocher3368]

Assumes cups can physically fit inside one another , unlike the other puzzles closer to logic.

[@atimholt]

The answer was instantly obvious, and there’s no reason to make it more complex than it needs to be. “Put one cup inside another” is as far as the discussion ever needs to go. I never would even have thought of putting coins in the bottom cup, and it comes across as superfluous to the actual answer.

[@elliotreid7401]

I like that. Better than my solution of 3 in each cup, put the three cups next to each other, and balance the final coin in the center. Each contains 3.3333 coins, rounding to 3, an odd number.

[@xnick_uy]

It can be explained faster why it is an impossible puzzle without resorting to out-of-the-box (or cup-in-cup) thinking: whenever you add two odd numbers the result is even. Then, if you have two odd number of coins in the first two cups, the remainder number of coins must be even, since when added to the first two must give 10, which is even; odd + even would be odd. This is similar to the explanation using x, y and z, but maybe simpler for a broader audience.

[@LivingChords]

There had to be a trick to it, so this is the first thing I thought of.

[@samarthmehta8732]

Please don't ask such riddles at parties.. That's the reason nerds get beaten up😂

[@hblake5213]

Except they're not really in the cup though all you have now is 1 cup with 5 coins in it, 1 cup with 3 coins in it and 1 cup with 2 coins and a cup in it, now I get that this is an infinitely arguably point but still.

[@MrBruhMan1746]

Put 4 coins in 1 cup. Put another cup into the cup. Put 3 coins in the cup that is inside the other cup. Put the remaining 3 coins in the last cup. The cup with another cup inside of it technically now has 7 coins and the cup inside it has 3 coins while the last cup also has 3 coins. Edit: called it

[@ohboy1113]

That partition trick at the beginning is really unnecessary and hard to do in your head. Think of it this way. Two cups have odd numbers. Those two odds always add to be even. Now the third cup is supposed to 1. Be odd 2. Add with the even number (the two other odds added up) and be even In order for this to be possible, an odd number has to add up with an even number to get an even number. That’s just not possible, so it has to be something with how you arrange the cups.

[@markgearing]

The next question: Is this a solution that a prospective employer would value, or would they prefer a candidate to quickly recognise that the problem, as stated, can't be solved?

[@MrGhosta5]

Depends on the person asking the question. One of my bosses would want to hear that it was impossible, one would want you to come up with an alternate solution, and one would ask just to troll you and only cared about how your responded to the question.

[@notsean9862]

The question we should be asking is why are the cups shaped like that

[@strifera]

I actually did figure it out, but only because I'd designed a similar puzzle before...also as an interview test weirdly enough. Mine involved moving rice grains from one cup to another using chopsticks though.

[@tverdyznaqs]

wow, mathnatitian partys must be so mutch fun!

[@ethansmith3734]

Math has to be precise. Math is a crucial part of engineering. Cheating it can result in failures with a variety of consequences

[@matthewryan4844]

Another variant of the solution is to put an odd number, say 7, coins in one cup and a second cup upside down on top of it to make a closed container and put the the other 3 coins in cup 3. No cup contains an even number of coins at any point.

[@Shadow4707]

I feel cheated.

[@lntelling6414]

I jokingly answered "what if i kept one inside another?" Turned out to be the right answer lol

[@ernestboston7707]

I find it odd that there are more thumbs down than thumbs up at this moment of writing this comment, 658 versus 659. I was able to figure out the same solution in about 30 seconds. Think outside the cup.

[@TonyCrenshawsLatte]

I knew almost right away that there is no way to conventionally divvy up the coins to fit the criteria. (because odd number + odd number + odd number will always equal an odd number.) So I figured the only way to solve it was by stacking the cups. But that sorta felt like cheating. So I was hoping the video would have a more creative, ingenious solution. I ended up a bit disappointed.

[@Deasen]

Can it be 0 and 3 and 7? 0 is not an odd or an even number so maybe this can be an answer too????

[@Roshkin]

I figured out the trick, but I thought it was breaking the rules, especially since not every cup fits into another

[@junkmail4613]

I immediately thought of 9 in one cup, zero in the second, and one in the third stacked upon the empty second cup, so we have 9, 1, and 1. QED

[@lukedornon960]

What if your cups don't nest though?

[@wenaolong]

I went with 7 and 2+1. Interesting, because here there is a rule that makes order of operation in addition "matter". In a certain sense, 1+2 =/= 2+1

[@assalane]

Meh. That's a stupid trick. A clever trick wouldn't go against the wording of the enigma. It expressively says an *ODD* number of coins in *EACH* cup. Placing a cup over another doesn't magically make the 2 coin cup become a cup with an odd number of coin.

[@Bramsen92]

so what the hell do you do if you get unstackable cups?

[@chakshujain7557]

Looks like interviewers have scarcity of puzzles, so they thought let's troll.

[@AW-br8gu]

I'm still trying to solve the 2 girls 1 cup puzzle...

[@barryisland5942]

Think in binary. Right-hand digits. 1 + 1 gives 0. 1 + 0 gives 1. Can't have three numbers that give a right-hand digit of 0. (Ten is 1010).

[@tosuchino6465]

Interesting solution. But it depends on the shape of the cups, doesn't it?

[@toddfarkman2177]

My solution was easier. I just pulled out a coin from my pocket and placed it in one cup. Then put 4 of the 10 coins in that cup as well. Then 3 coins each in the remaining cups from the 10. Hey, you didn't say I couldn't. If you're going to bunch up the cups, the least I can do is pull a coin from my pocket!!

[@Paulafan5]

I got that cheat answer too because the cup in a cup is a cheat too.

[@Manabender]

My solution: 0+5+5, put cup 2 or 3 in cup 1. Now, not only do they all have an odd number, they also all have the same number. ELEGANCE!