Can you solve the famously difficult green-eyed logic puzzle? - Alex Gendler

  • Опубликовано: 16 июн 2015
  • View full lesson:
    One hundred green-eyed logicians have been imprisoned on an island by a mad dictator. Their only hope for freedom lies in the answer to one famously difficult logic puzzle. Can you solve it? Alex Gendler walks us through this green-eyed riddle.
    Lesson by Alex Gendler, animation by Artrake Studio.

Комментарии • 8 137

  • raye
    raye 7 часов назад +1

    i would probably just say, "100% GREEN." i mean, it's not new information. the color green is 100% green. i would just hope with them being perfect logicians they'd at least take a hint as i aggressively point at them all.

  • Shannon Alex
    Shannon Alex День назад

    Actually, eye iriss' are actually reflective, so they could stare in each other's eyes and tell.

  • Jamie Frostbyte
    Jamie Frostbyte День назад

    If there are water containers, then they could have spilled the water (refill then repeat) to see their own reflection and even can see their eyes

  • Apex Predator
    Apex Predator 4 дня назад

    This is an illogical scenario, therefore it cannot be answered logically.

  • Henry Gengler
    Henry Gengler 5 дней назад

    1:17 What can you say... EXCEPT YOU'RE WELCOME

  • ChoBoi Chobani Gaming
    ChoBoi Chobani Gaming 6 дней назад

    I would have brought extra reflective glasses and said look into my eyes the key to wisdom

  • Xmy Hee
    Xmy Hee 7 дней назад


  • Yoonseong Do
    Yoonseong Do 7 дней назад

    ok the thing is that nose doesn't look like nose at all

  • Tofu Kingpin
    Tofu Kingpin 8 дней назад +2

    Damn it Carl why you gotta be the third wheel

  • Hilary Denham
    Hilary Denham 8 дней назад

    Good work dood

  • ??? ¿¿¿
    ??? ¿¿¿ 9 дней назад

    There's an opaque water what brand!

  • Diptanil Roy
    Diptanil Roy 9 дней назад

    just look at the sea water..... easiest possible way

  • Penguinspy !
    Penguinspy ! 10 дней назад

    After the hint that the girl said i would have looked at all the other people and saw that they had the same colored eyes, so that means i had the green eyes. But nnnnooo it had to get logical.

  • Game Fox
    Game Fox 11 дней назад

    dump water look at floor.

  • TerielAtmano
    TerielAtmano 12 дней назад

    There's something I don't understand.
    There are two levels of knowledge here:
    1) Do I know that there's at least one person with green eyes?
    2) Does I know that everyone knows there's at least one person with green eyes?
    Both of this have to be answered positively for the solution to work.
    When there's two people, everyone knows 1), but they can't know 2). That's because 1st person may think they have brown eyes, and therefore they think that the 2nd person (not knowing they themselves have greens eyes) thinks there isn't a single person with green eyes.
    When there's three people, there's still a possibility that not 2) is not positive for everyone. Let's look at it from the perspective of the 1st person. They think they have brown eyes, and they're trying to imagine what the 2nd person is thinking. And 1st might be thinking "This poor sap, 2nd, thinks he's got brown eyes, and he sees my brown eyes, and therefore he thinks 3rd is looking at two sets of brown eyes. If that is true, then 2nd can't assume 3rd is even aware there's anyone here with brown eyes. Therefore I can't assume 2) to be correct."
    It breaks down with 4 people, because it's obvious to everyone that everyone sees at least one set of green eyes, so 2) is positive for everyone.
    So my question is, if there are 4 or more people, why didn't they just start counting the days themselves the day they came on the island?

  • silvja silvja
    silvja silvja 13 дней назад

    Game theory!

  • CosmicGumballz
    CosmicGumballz 13 дней назад

    lol I have green eyes

  • Silly Squirrel
    Silly Squirrel 14 дней назад

    I'm so happy that I created a solution :-)

  • Oli K
    Oli K 14 дней назад

    Why not say "the person next to you has green eyes"? Its not new knowledge but they'll realise it's true for all of them

  • erika medina
    erika medina 14 дней назад

    But couldn't the kids pour the water on the ground and see thier reflection?????

  • Diana Henne
    Diana Henne 14 дней назад +1

    Or just, y'know, tell them to spill some water and look at their reflection in it

  • The Chosen One
    The Chosen One 15 дней назад

    Or i could say all of you have green eyes

  • Pommy Wolf
    Pommy Wolf 15 дней назад

    Wow, if they are amazing at math and all that stuff, they would need access to uh... idk, paper? Don't you think that would help them A LOT in their grand quest to freedom. If not, just us a rock to etch it in the dirt or something! If they dont know how to write letters, let each prisoner have a number instead of a name. Maybe say "1=✔" to indicate that prisoner one has green eyes. Use your finger and point to the prisoner that is number one so they could know. Also, why didn't they have someone point at each other, and do some sort of signal to indicate they have green eyes? OH, ITS BECAUSE MUTE PEOPLE CANT INVENT SIGN LANGUAGE!! XXD

  • It’s Colossus
    It’s Colossus 15 дней назад

    If you know your parents then you would see if they have green eyes but then you see everyone else parents with green eyes and all of there kids have green eye so you would guess you have green eyes there home sweet home

  • It’s Colossus
    It’s Colossus 15 дней назад

    How do they know what the colour green looks like

  • Emily Wu
    Emily Wu 15 дней назад

    I just love these riddles. I get a brain fart every time after they tell you to pause it, so I rewind the video. It makes so much sense after! They're really good boredom busters, too!

  • Sara Ziegler
    Sara Ziegler 15 дней назад

    Me: Oh, the pattern will repeat, eh? Well, same as the pattern of people. IT IS THE SAME PEOPLE.
    3:19 or something.

  • YodaIAm69
    YodaIAm69 16 дней назад

    If they could ask to leave then they could’ve said stuff to the other inmates

    • YodaIAm69
      YodaIAm69 16 дней назад

      And they could probably just point at someone’s eyes and do a thumbs up to show that they all have green eyes

  • Maha A.S.
    Maha A.S. 16 дней назад

    Can't you say everyone you look at has green eyes cuz it's not new

  • Kyle Suozzo
    Kyle Suozzo 16 дней назад

    Who else just watches for the answer

  • dlgrauman
    dlgrauman 17 дней назад

    The fact that the islanders haven't solved the problem without you indicates that the islanders are not aware that the other islanders are, like themselves, perfect logicians who want to leave the island as soon as possible. Because they do not know this, and because you are not allowed to tell them so in the announcement, your announcement will not provide give them all the information they need to solve the problem. The mad dictator wins!

  • Crazy Cheeksqueek
    Crazy Cheeksqueek 17 дней назад

    Bruh isn’t there water in the ocean. Just see through the water, BOOM.

  • Cocoa The Cat
    Cocoa The Cat 17 дней назад

    "All water is in opaque containers"
    Wot about the toilet..

  • cloudsweapon567
    cloudsweapon567 18 дней назад

    I would shoot the dictator

  • Meggie The Fluff
    Meggie The Fluff 18 дней назад

    What about "at least 98 of you have green eyes"???

  • Guns And Squips
    Guns And Squips 21 день назад

    How about "The person beside you has green eyes" ? It wouldn't be new information, since they can all see that, but, since everyone is next to someone else, they'd be a 'person beside', therefore they'd know that they have green eyes too. Plus, it would save a ton of time

  • Meowthful 127
    Meowthful 127 21 день назад

    But the dictator has glasses....

    Reflective surfaces

  • Heidi Lavender Animals
    Heidi Lavender Animals 21 день назад

    No way to learn their eye colour there is litterally water

  • Pseudonymous
    Pseudonymous 21 день назад

    Whats the point of saying water is in opaque containers?

  • Heidi Lavender Animals
    Heidi Lavender Animals 21 день назад

    If you told them at least one of you has brown eyes then everyone will think they are the one because they can see the other 99 people have green eyes and everyone will just stay there if there was only one night that would be kinda funny

  • MC cashMax
    MC cashMax 21 день назад

    Here's a much simpler solution:My statement: "The prisoners around you have green eyes"My Reasoning: It's one statement and it no new information to any single prisoner, they already know they're surrounded by people with green eyes. However, it's useful because if a prisoner (a) is told this in a crowd of 99 other prisoners, "The prisoners around you have green eyes" then Prisoner a would know, another prisoner (b) would know all the prisoners around prisoner b has green eyes (including prisoner a). Therefore all 100 prisoners using this logic knows he/she has green eyes and escapes the next day. EASY

  • Robert Smith
    Robert Smith 21 день назад

    What if half of them were color blind?

  • Leader Leo
    Leader Leo 21 день назад

    Why dont they write down what eye colour others have?

  • Darcy Lyon
    Darcy Lyon 21 день назад

    Just say “if I was all of you, I would have left by now.

  • nrenderkatolik
    nrenderkatolik 23 дня назад

    how about saying that everyone saw everyone elses green eyes (because they could see during role)

  • Tom Vet
    Tom Vet 24 дня назад

    Telling them that at least one of them had green eyes was new information. If they had already known it they would have been gone long ago.

  • Lee Bagley
    Lee Bagley 24 дня назад

    Why does she have a Stache :
    XD 2:18

  • Lord Hawkeye
    Lord Hawkeye 26 дней назад

    Everyone on this island would have already been long gone by now if we follow this riddle's logic to it's conclusion because each and every one of them ALREADY knew at least one had green eyes.

  • The Roblox gamer I my nick is matijos on roblox

    Lucky me (green eyes)

  • Antonia Sadlek
    Antonia Sadlek 26 дней назад

    Lol I have green eyes.

  • WingedBunny
    WingedBunny 26 дней назад

    I would be the lone blue eyes person who has to stay there for the rest of my life

  • WingedBunny
    WingedBunny 26 дней назад

    I would signal to people with my eyes during head count.

  • Harry Potter Fans
    Harry Potter Fans 27 дней назад +1

    They could’ve just looked in each other’s eyes
    Because if you look into a differnt persons eye you can see yourself in there, eyes are basically mini mirrors

  • SimsulatedId
    SimsulatedId 27 дней назад

    "At least one of you has green eyes" sounds like 'new information'. As the dictator, I'd probably torture you and retract my offer to the Islanders - perhaps chop a few legs off, cut rations.... You blew it! But it's still an interesting puzzle.

  • Choi Bruce
    Choi Bruce 27 дней назад

    In the simplification with only adria and bill, it seems one of them concluded that the other would have left upon seeing non green eyes and so because the other didnt leave that must mean his eyes are green. There's a problem I think in this as no one on the island knows what colour green looks like so how would they know that the theoretical non green colour actually IS a non green colour? it's not like the islanders know EVERY SINGLE COLOUR in existance EXCEPT green and even still in THIS scenario they would be able to conclude that everyone's eyes are green with process of elimination. They must know some colours but not all, so they can't really conclude that a colour they dont know is not green.

  • Qwerty O v O
    Qwerty O v O 27 дней назад

    I would say " You All Have Green Eyes"

  • Bradley Huffer
    Bradley Huffer 27 дней назад

    What if you opted to lie to the crowd, thereby imparting no new information? “Exactly 99 of you have green eyes.” Every person walks off depressed as they now believe they are the one person without green eyes. The following day everybody wakes up to a full crowd. The only way that would happen is if each person saw 99 people with green eyes, meaning everybody has green eyes. The dictator couldn’t even run up to the microphone and say “That’s a lie,” as that would give away everybody had green eyes.

  • Zay Williquette
    Zay Williquette 27 дней назад

    My answer was "None of you have ever seen someone who doesn't have green eyes"

  • KerbalTube HD
    KerbalTube HD 28 дней назад


  • sarcasm ساركازم
    sarcasm ساركازم 29 дней назад +1

    What's if I lie and said one of you have a different eye colour. That would be more simple and quick

  • Billiam Cipher
    Billiam Cipher 29 дней назад

    Just say the person next to you has green eyes

  • ; h o p e.
    ; h o p e. 29 дней назад

    why does he not want them to leave

  • Allpha KUN
    Allpha KUN 29 дней назад

    Can some one explain where I'm wrong?
    Wait, if there are three people and each one sees two green eyes. They would think they don't have the green eyes as the person said at least 1 so it might only be 2. With like a 100 people, they will see 99 green eyes and would be even more unsure and wouldn't leave

    • Andrew C
      Andrew C 14 дней назад

      Each person is keeping track of who should have left but didn't. It's easy to see the argument with two people, but hard do see how 3 or more play out. The concept is mathematical induction and is famously brain bending. The reason why they stay until the last day will eventually boil down to "if this one last person with green eyes doesn't leave, then I must have green eyes too". With each day that passes, they realize that one additional person is confirmed to have green eyes. They just don't know if it's themselves. after 100 days, the number of confirmed people is 100 which includes themselves so they all leave at that time. How does the number of confirmed green eyed people increase by the day? Look at two people. On the second day, they expected the other to leave. Since the other person didn't, they knew they both had green eyes. Now look at three people. since person 3 would only see 2 people with green eyes, he would expect the first two to leave on the second day (because of the 2 person argument). Since the other two stayed for the third day, that leaves only one reason: Person 3's eyes are green too.
      now look at 4 people. Person 4 would assume that the three others would leave after 3 days (See the 3 person argument). Since they didn't, it means person 4's eyes are green too. and so on up til 100 people.

  • Aaditya Dahal
    Aaditya Dahal Месяц назад

    Pff this is easy
    just pour the water on the floor and see if your eye is green

  • Lucky Tree
    Lucky Tree Месяц назад

    how do people EAT?!?!?!

  • TheWierdSideOfTheInternet
    TheWierdSideOfTheInternet Месяц назад

    2:46 CORAL!!!!

  • Thomas Tran
    Thomas Tran Месяц назад

    Id say: "Everybody around you has green eyes"

  • Awesome Dogs
    Awesome Dogs Месяц назад

    I know how to easily beat this look deeply in their eye it will show what there looking at which is you

  • The Pencils
    The Pencils Месяц назад

    At least 99 of u has green eyes

  • DiamondKittenK Kat
    DiamondKittenK Kat Месяц назад

    Can they do hand signals? Then they can just point to other peoples eyes and thumbs up lol

  • Warrior 747s
    Warrior 747s Месяц назад

    My message would be
    “Please pour some of your water on the ground and look at it”
    BAM, 100 people got out of the island in 1 day

  • dailypuzzle cheats
    dailypuzzle cheats Месяц назад

    Its very difficult to solve. You can find free puzzles cheats here

  • Bleuberriii
    Bleuberriii Месяц назад

    Isn’t death by someone else’s hand also considered freedom from living?

    No, I’m not depressed, that’s just how i see it

  • Jenina Huang
    Jenina Huang Месяц назад

    *gets green contacts

  • Jenina Huang
    Jenina Huang Месяц назад

    This literally became my second favorite riddle! (first is The Bridge Riddle)

  • Ayla Tirocchi
    Ayla Tirocchi Месяц назад

    She also could've said "everyone around you has green eyes" This isn't new information because they can obviously see that it is true. Also she is saying it to everyone , that means know that for eg.Gerry sees all green eyed people

  • The Dank Lord Of The Sith
    The Dank Lord Of The Sith Месяц назад

    If it's on an island, you can look at the ocean no?

  • The Dank Lord Of The Sith
    The Dank Lord Of The Sith Месяц назад

    First of all, why is this even happening

  • The Dank Lord Of The Sith
    The Dank Lord Of The Sith Месяц назад

    I'd break out and then scream to all

  • adem hoshigake
    adem hoshigake Месяц назад

    The horses name was Friday.

  • John Randomness
    John Randomness Месяц назад

    Probably mentioned before, but this could foul up their reasoning. Since they all can see 99 green eye pairs, and know that everyone else can see either 98 or 99 eye pairs, someone might be able to figure out that there is a reason behind an apparently bizarre statement like, "At least one of you has green eyes." If he figures out that they're not supposed to be told anything they don't already know, then he might deduce that if exactly two persons had green eyes, they would both leave the first night -- or maybe one would leave the first night. The person(s) leaving would deduce that since they were told at least one person had green eyes, and not present any new information, then everyone would already see at least one green eye pair, which would mean that at least two had green eyes.

  • Salvador Magana
    Salvador Magana Месяц назад

    What bothered me is that if the first line on their face a nose and the bottom one the mouth or is the first line at mouth and the bottom the chin

  • Quinlan McLemore
    Quinlan McLemore Месяц назад

    The 2K people who disliked this were the guards on the island

  • kinnari Chunekar
    kinnari Chunekar Месяц назад +1

    Write on the soil duhh!!

  • person yea
    person yea Месяц назад

    Simple i would say: You all have green eyes.

  • Emre Unal
    Emre Unal Месяц назад

    Just pour the water on the ground and see your reflection. You could also say, ALL OF YOU HAVE GREEN EYES! Then get the freak outa there

  • Saiko Xll
    Saiko Xll Месяц назад

    I don’t get it, would of just said go for it ya’ll die anyways.

  • King Aragorn II Elessar of Gondor
    King Aragorn II Elessar of Gondor Месяц назад +1

    You're standing next to someone with green eyes

  • zarconeus
    zarconeus Месяц назад

    This example does not work. You can't make an assumption on a group of two out of three and apply the green eye logic to that group. You must apply it only to the entirety of the islanders, minus the guard and the dictator.

    • zarconeus
      zarconeus Месяц назад

      It cannot be re-applied each day unless the person came each day to tell them.

  • Hemanth Dalmia
    Hemanth Dalmia Месяц назад

    We could also say all of them had same coloured eyes

    SKYLUKAS Месяц назад

    couldn't i just say:"go and ask the guard!"

      SKYLUKAS Месяц назад

      Nolan Chojnacki I know But they should just ask to get out and they both will, if they just go to the guard and ask if they can get out. They should not ask for their eye color but just to get out, that's what I've meant.

    • Nolan Chojnacki
      Nolan Chojnacki Месяц назад

      SKYLUKAS. The guard wouldnt tell them...

  • Maya Ike
    Maya Ike Месяц назад

    I wonder what does simoltainios mean

    • Andrew C
      Andrew C Месяц назад +1

      Simultaneous = at the same time

  • Maya Ike
    Maya Ike Месяц назад +1

    If the dictator has a knife get it kill I'm n go

  • Scott Moore
    Scott Moore Месяц назад

    Just one question: if they’ve been imprisoned since birth, how would the dictator have known they were perfect logicians?

    • Nolan Chojnacki
      Nolan Chojnacki Месяц назад

      Scott Moore. When did it say he knew

  • IIChamp's GalaxyII // KChampion
    IIChamp's GalaxyII // KChampion Месяц назад

    What if they do not know what green is?

    • Andrew C
      Andrew C Месяц назад

      That got me too at first, but then I realized that doesn't change the logic. in fact it helps the puzzle. I was always wondering why they didn't leave a long time ago (100 days since the rule was implemented). It wasn't until they heard the statement at "at least one of your eyes are green" that they learned that the color they were seeing might be green.

    • IIChamp's GalaxyII // KChampion
      IIChamp's GalaxyII // KChampion Месяц назад

      I meant if they did not know what the color green is,
      they may think blue is green...

    • Nolan Chojnacki
      Nolan Chojnacki Месяц назад

      IIChamp's GalaxyII // KChampion. They probably do... I mean theres plants around the island

  • Mark Munroe
    Mark Munroe Месяц назад

    me: "the person next to you has green eyes" they would know the person next to the person next to them has green eyes witch means they have green eyes

  • mops9
    mops9 Месяц назад

    If I become that dictator, I would say, you can’t say anything about their eyes, checkmate

  • Kenyon papen
    Kenyon papen Месяц назад

    You can tell them your friend has Green eyes

    • Nolan Chojnacki
      Nolan Chojnacki Месяц назад

      Well who said all of them are friends, what if none of them are friends

  • ; h o p e.
    ; h o p e. Месяц назад

    Why does he not want them to leave? °-°

    • Nolan Chojnacki
      Nolan Chojnacki Месяц назад

      Bluє Príncєѕѕ •. No answer, its just a riddle with some realism to make it understandable

  • GoldenBoi52
    GoldenBoi52 Месяц назад +1

    Hey i know another way doesnt the eye reflect so if i look at another persons eye i can see if mine is green