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

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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.

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44 Responses

  1. It's David says:

    I’d say thumbs up for green eyes and so on…


    Doesn’t water reflect light too?

  3. Carlo Ciotola says:

    They can simply control their eye color in another person eye reflect

  4. Larsen Villaranda says:

    Now if only we can use this to those North Koreans.

  5. john roliven blan says:

    I'll just make hand gestures

  6. isaac27581 says:

    that makes no sense, if there are 3 people, you already know that each person has seen another green-eyed person

  7. Cyclops says:

    I’d just go if all people have green eyes I’d assume I have green eyes

  8. Agastya Ray says:

    Nahhh id just look in someones eye,look at the reflection on their eye and see if my eye is green.

  9. Pitabread Singalong says:

    but like, isn't telling them that at least one of you has green eyes new information? Since they dont know if anyone amongst them has green eyes.

  10. Rinada Grace says:

    Or they could just… clean a plate and look at their reflection, or pour the water into a bowl and see……..this riddle had a lot of flaws..

  11. Hxhx Vxhx says:

    "The person next to you has green eyes" boom easy non rule breaking statement

  12. North American Mapper says:

    I have blue eyes I can’t leave 🙁

  13. Rob Harrison says:

    I don't get it, in the example at 2:50 why does it matter if they see two green eyed ppl or just one. If I'm one of them in that example and I have green eyes or brown eyes, they both see at least 1 person with green eyes (which is not new information).

  14. roger dickens says:

    The di-ctator eventually kills all the prisoners before night hits. Thus no-one will risk trying to leave.

  15. عزوز آلعلي says:

    من عربي

  16. Dragill The alchemist says:

    Wait what if someone falls and the water pours out of the bottle and deny see

  17. Paul Berg says:

    There should be a SPOILER alert for people who actually want to solve the puzzle. This video says the answer at 1:44.

  18. Mushoku Kame says:

    lets say were adria and we can be greeneyed, or browneyed. we do see 2 greeneyed people. if we are browneyed, bill will see one greeneyed and one brown. but since the statement says at least ONE person is greeneyed, he will never be sure, because maybe carl is the only greeneyed. same goes for carl the other way around. do i miss something? in my thinking, no one will ever leave, no matter how many days go by.

  19. Ayesha Mulla says:

    I would just straight away say “everyone has green eyes” and even if the mad dictator gets angry at me and throws me into the volcano, at least I saved a hundred people lol

  20. Ruud Lenders says:

    All joking in the comments aside, I seriously wonder this. Why does announcing that "at least one of you has green eyes" change anything? Everyone already knew that everyone could see at least one prisoner with green eyes. I understand the logic of waiting 100 days, but if all prisoners are logicians they could have started their waiting game long before someone with a microphone showed up.

  21. Iamnotacommenter Luo says:

    Can’t you look in the reflection of somebody else’s eyes?

  22. Flarbargason says:

    You didn’t say you were going to give the answer! You just said it before I knew you were done explaining!

  23. YeMi - Gaming says:

    They can’t talk but they can nod right…

  24. Euphoric Host says:

    Make one statement 'you all have green eyes' xD

  25. AviatorAvis says:

    "Everyone rip out one of your eyeballs."

  26. Dilan Abdulla says:

    They can look into each others eyes to see their own eye colour. Also, they can look into the toilet water (A toilet was shown in the video).

  27. Chewie_Swag says:

    My soloution spill my water on the ground and use the reflection

  28. Jude Arubio says:

    How about just let them act like they drop their water, then the water might reflect on them.

  29. Ayan Chavan says:

    The most famous puzzle is one that involves 110 prisoners

  30. Rick James says:

    Couldn't they just as easily thought that the reason the other people didn't leave is because they don't know they have green eyes. I think the bigger clue was the fact that everyone around them had green eyes.

  31. Hien Duong Van says:

    say "at least 99 of you have green eyes" and they all will escape after 2 days

  32. QazwsxrfvT says:

    Actually this can only apply to 2 people, because all of them would be starting comparisons themselves, and since there are 99 other people, they see more than one with green eyes; even after the second night with 3 people they can't get any info, since who the heck is comparing with who?

  33. Pizza Cat says:

    also known as north korea

  34. Deadpool's Maximum Effort says:

    Well, how would they know that Green is a color or what really is green if, they haven't communicated and educated?

  35. 바나나 says:

    if there is one mirror in this island, no one would rested in here.

  36. Adam Turner says:

    I figured it out

  37. Della Lewis says:

    You can see yourself in other people's eyes. So…………

  38. Taki Eddin says:

    "If you don't have green eyes you are immortal" done.

  39. Svízel přítula says:

    If you say "At least 99 of you have green eyes", they can escape the next night, because if one didn't have green eyes, it would be new information.

  40. Kiera Nicely says:

    Depends what you mean by new information – to them? or in general? Because if I said "I've all always had green eyes" then would that be NEW information… if it's always been true?

  41. SirpentPlayz says:

    Just say at least 99 of you have green eyes

  42. Green the Ninja says:

    “just pour out water and look in your reflections”
    or "All of you have the same eye color"

  43. 영국산홍차 says:

    What if I say, “At least 99 of you have green eyes.”?

  44. 정현우 says:

    석방 요청할 때 두 명이서 짝 지어서 가보라고 하면 되잖아요~

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