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The famously difficult green-eyed logic puzzle - Alex Gendler



View full lesson: http://ed.ted.com/lessons/the-famously-difficult-green-eyed-logic-puzzle-alex-gendler

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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Runtime: 4:42
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Comments:

Author Meppers JR ( ago)
I still don't understand what he's saying

Author xXeditzXx ( ago)
Break the bottle and just said it dropped........

Author Solcoolman ( ago)
I would've said: "Get logic idiots."

Author mutate 9601 ( ago)
You said they can't communicate and on 2:38 you said they tells each other

Author David Spring ( ago)
I would have said "you all have green eyes" because that's not new information, they just couldn't communicate it.

Author Pandora the Male Leopard ( ago)
you outsmarted the dictator by saying one of you has green eyes so the prisoners asked if they could leave to see which one had the green eyes

Author Kitten Jibanyan ( ago)
No I can't solve this riddle
There is no logic

Author The gamer Bro ( ago)
They could have all looked in each other's eyes carefully and found out

Author Martín Gonzalez ( ago)
Hahahahahaha that's really clever

Author Zhao Xian Ng ( ago)
Pour water on the floor that's reflective madafuka

Author Rainbow Clouds12 ( ago)
" as it is, all 100prisoners have green eyes" talk about racism to the max, LOL

Author lucky girl ( ago)
OH YES I GOT IT CORRECT FOR THE FIRST TIME.

OH NOOOOOOOOOOOOOOOO I ALMOST DID EVERYTHING CORRECT BUT I NAMED THEM KATE AND TOM... THIS IS UNFAIR.😔😔😔

Author PRGME7 ( ago)
Why would the dictator teach colors to the prisoners

Author Carlos Rios ( ago)
I'd say "Each of you find one different person with green eyes and stare at them." Then there would be 50 pairs of people staring at one another, each one realizing they're being stared at because they have green eyes. Off the island in a couple minutes.

Author Ragesh G.R ( ago)
everyone knows that atleast 99 have green eyes. so all could have left the 100th day after they became sentient enough to understand logic. the announcement was not at all required

Author janghoon lee ( ago)
Then there's the guy that's color blind. Feels bad man

Author Ms Cristina's Shop ( ago)
One green eye! Seriously! I would see 99! So its a lie!!!!!!!!!!!!!!!!!!!!!!

Author Ella G ( ago)
Unless you have brown eyes and nobody kept track of that for 98 days.

Author 92axelmaster ( ago)
Or you could call in SEAL team six and liberate the island.

Author Kimmy Jo ( ago)
point to the grass, point to your eyes and and wait for a nod...seems simple enough

Author Tenor Ong ( ago)
Didn't they alr know at least 1 have green eyes they see 99 people with green eyes every morning

Author nathan cao ( ago)
but what if they're all to dumb too know that

Author meow 3756 ( ago)
How can you be a logition as a prisoner on a deserted island

Author . ( ago)
When the video started I thought he was talking about Cuba.

Author Christopher Bacha ( ago)
everybody watching in 2017 like this comment

Author Jareth Klaassen ( ago)
the mad dictator has no weapons, as they could be too shiny. therefore, all you need to defend yourself from the dictator is skill and a sword. which means, you could say "at least 99 of you have green eyes" without dieing.

Author 49ducks Gaming ( ago)
now listen up this is confusing,you tell them they all have green eyes now this is new information, to some because technically it works.

Author Apotre Mosko ( ago)
didn't get this one..

Author much As you want ( ago)
I would just take my chances, and just asked to leave from the beginning

Author Michael Le ( ago)
i would have said i like your eyes that would have helped them know if they have green eyes or not

Author Mary Rachel ( ago)
There is a 100% chance that I have green eyes, because I don't live in such a cruel and bias prison.

Author Dylan Memes ( ago)
This is probably the easiest riddle they have put out

Author JORDAN KRISHNAYAH ( ago)
The dictator is trump

Author Megan Amato ( ago)
Why can't they say everyone around you has green eyes?

Author coblestoneBoom ( ago)
Adria and Bill. I ship it.

Author Izzy Haddad ( ago)
God I love ASL (American Sign Language)

Author Spark Animations ( ago)
can I just use hand motion

Author Creepy Betty ( ago)
If they are on the island, they could just look in the ocean

Author Evo- Un ( ago)
Nobody told them that they could leave if they had green eyes

Author Maverick Wang ( ago)
Just look at other people eyes.That is a reflective surface

Author Twisted Code ( ago)
I stopped understanding when you added the 3rd person. Could someone ELI5? I'm normally decent with logic puzzles, but this puzzle has me puzzled more than most puzzles puzzle me.

Author Rob Wilks ( ago)
Could have said, every prisoner u see has green eyes👌

Author Eumir Homeres ( ago)
what if u just siad "All of u have green eyes"???

Author Holly does......... ( ago)
Why don't they just communicate with sign language?

Author CrestedAmy ( ago)
the prisoners could have pointed to the anything green and then point at the other person till they understand.

🌳➡👧👦👧👦➡eyes arrow=the person pointing

Author Steve jenkins ( ago)
CORAL

Author Steve jenkins ( ago)
Couldn't one of the priosners just grab a leaf, point to another prisoners eyes

Author Vortex Of Rainbows ( ago)
What if you look into someone else's eyes, then you can see a reflection (Kappa)

Author RedX_16 ( ago)
wait if they didn't talk since birth then that means they don't know how to talk... so they dont know how to understand other people! simple logic

Author :v ( ago)
I have green eyes

Author :v ( ago)
I have green eyes

Author Jack Hacker ( ago)
i know the answer, viva la revolution!!!!!

Author Loc Thomson ( ago)
If i was on the island, I would have thought if everyone else had green eyes, I wouldn't be an exception. Then I would get shot for trying to break out anyway.

Author UnicornBlingThing ( ago)
Only green green eyes can leave? ONLY GREEN EYES?



*That's rasist.*

Author PRNTSCRN ( ago)
I think they can go home even the first day ;)
If you would tell them: The person / persons next to you has /have green eyes? (This is not information they don't know, and they can immediately reflect it to themselves).
Because this is true for everyone.

Author Pineapple Kyle ( ago)
Knowing dat I could have a green eye 1/100 chances is enough for me to yolo ask the guard xD

Author Astralflight Warriors ( ago)
So, I don't see why they couldn't dump water into their hand in order to see their eyes. They were clearly drinking out of it so water could obviously come out.

Author Owen Bartels ( ago)
If they can't speak then how do they ask to leave?

Author CaptainROFL ( ago)
couldn't you say something like, 'poke everyone you see with green eyes' and then everyone would get poked, and leave the island over night

Author RoseQuartzPanda ( ago)
But... But what if they don't know that they're all perfect logicians?

Author NotsoEthos ( ago)
but would they know what green is?

Author Twin Blade Volt ( ago)
Wouldn't it be weird if literally EVERYONE had green eyes. Like if I saw everyone had green eyes I'd assume I'd have green eyes and leave.

Author The Wot Blitz Gamer ( ago)
You can look into someones pupil and you reflexion is there and then they know if they are green eyed

Author XxHatterxX ( ago)
BITCHES GOT ARMS LIKE SLENDERMAN

Author Tilda Larsson ( ago)
Stop spoiling everything before I have paused

Author _Shattered_ ( ago)
that complicated explanation was unnecessary because if they are smart they will solve it without your statement btw thats not new info, you can just push someone to the exit (probably your friend because they trust you) boom that easy and the last person is next to the second last because they are arms on shoulders pushing each other

Author _Shattered_ ( ago)
i would have said for everyone to get in a line besides one person give the people with green eyes a 1 and within 1 night everyone is gone because the person not in line can point at them selves and gesture for there eye color by pointing at their eye

Author Pieces297 ( ago)
What's with the hitler moushstache

Author SimplyGaming24 ( ago)
Or... you could just pour some water on the floor and look into it, cuz water is reflective...

Author Roann Houngue ( ago)
Or you could tell them that there is an even number of people with green eyes, they would then realize that if they see 99 people with green eyes, the 100th person (themselves) should have green eyes as well

Author Owen Bartels ( ago)
Wait in the beginning he said: IMAGINE an island. So that mean imagine all the prisoners are idiot and really want to get off the island

Author QuaticL ( ago)
They are on an island. Isn't water reflective?

Author Dragonoidalpha ( ago)
The prisoners could have looked at their reflection in the water XD

Author coblestoneBoom ( ago)
If I had just said that "at least 99 of you have green eyes", because that is not giving them new information. They see the other 99 people on a daily basis, and they would know that all 99 of them have green eyes. Everyone would've been gone within two days, because once they see that no one else has gone, they would know that they also have green eyes, because everyone was thinking the same thing.

Author ArceusPower101 ( ago)
did you know that less than 2% of people actually has green eyes?

Author Emily Davis ( ago)
Or what if you said 'You can leave the island'.  They already know the possibility of them leaving but this confirms it.

Author Rickity Sticks ( ago)
Spill the water? No? Eh try the hard way.

Author Lily cat ( ago)
I would say: Spill water on the ground and look at it.)

Author Alex Wheeler ( ago)
wouldn't another solution just be, "everyone around you has green eyes" since it is said to all of them at the same time, that must mean that the statement applies equally to everyone. therefore, everyone must know that they have green eyes.

Author Pancakeman1234 ( ago)
couldn't you just say that "everyone you see has green eyes"?

Author Mr.goose Goosersom ( ago)
the statement "at least one if you has green eyes" suggests that the number of people with green eyes must be greater than or equal to 1. Considering that everyone can see each other, they can conclude that if everyone have green eyes, I must have green eyes.

Author Aryan Saini ( ago)
1:18 use a giant run on sentence

Author Owen Bartels ( ago)
Just say "The person to your left and right as green eyes" it's not new information

Author Warrior Army ( ago)
I got the second way so I'm the best

Author truthless47 ( ago)
The funny part about this one is that it assumes a high level of intelligence of the people you're trapped with. Personally, I would assume none of the other 99 could make logical deductions like that, and never leave.

Author randomyoshie ( ago)
Couldn't you have said the people next to you have green eyes

Author The Pokemasters ( ago)
You could also say "the person beside you has green eyes"

Author Tony Scimeca ( ago)
This one kinda sucked.

Author Astra CS:GO ( ago)
It really should be easy, just look at everyone so you see that they have green eyes. Then what is the chance of you not having green eyes too?




Spoiler: Small

Author lord bacon ( ago)
couldn't they just see their reflechtion in other people's eyes ????????

Author Discord Is Best Princess ( ago)
You can see your reflection in other people's eyes... also you can pour the water on the floor

Author irura nganga nyiha ( ago)
Why can't you say...
Look at your partner and nod to me if they have green eyes
Assuming there are an even number of aliens, everybody would nod, thus proving that they all have green eyes
Also, they are not technically communicating with each other but with me, since I told them to nod at me.

Author I_am_boosted ( ago)
High five some one if you have green eyes

Author Norcalflat ( ago)
"Attention North Koreans, at least one of you have green eyes."

Author Jade Choy ( ago)
Would" if anyone you see has green eyes, give them a pinch." Work?

Author Get / Here ( ago)
You don't know who's watching who though?

Author OnEpIeCeLuFfY9 ( ago)
What is fun is the dictator, any other sentences i found, fiven the ´´danger´´ that the dictator represents for me is not valid. But I only spent 3 mins thinking, anyone tought another way? I tough a few like: only 1 person in this island doesn´t have green eyes or there´s at least 1 green eyes person front, back or by your side...

Author Zoë Zaki ( ago)
Okay? It works with three people but it doesn't work with 4 people. This is dumb.

Author Ittikii OwO ( ago)
What if you said, "Everyone you see has green eyes."

Author TrollandNoob ( ago)
They can look into each other's eyes

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