Can you solve the famously difficult green-eyed logic puzzle? - Alex Gendler
15,774,002 Views
32,752 Questions Answered
Let’s Begin…
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.
Create and share a new lesson based on this one.
About TED-Ed Animations
TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »
Meet The Creators
- Educator Alex Gendler
- Director Outis
- Narrator Addison Anderson

by TED-Ed
Can you think of some real-life situations where our second-order knowledge and third-order knowledge about what others know makes an important difference?
Comments are closed on this discussion.
Aditya Pasbola
Lesson completed
yes actually we can think of them in daily life
veronica Pinales
Lesson completed
Rumors start spreading about a specific person and you really don’t know who’s the right one
Carlee Collison
Lesson completed
If 6 teams are in a basketball tournament and they claim they will win, who actually won?
Sloane Taylor
Lesson completed
If ten people think they have the golden ticket, who actually has it?
Hikaru Tamashiro
Lesson completed
When trying to see which person is lying to you and which one isn't.
Dorian Marié
Lesson completed
Where there is a secret, you are in a group of 10 people for instance, and people can leave the room only when they are sure they know the secret, e.g.: "it's time to eat". Except that they are not sure if everybody knows the secret.
But then one person comes in and say "Oh John you look hungry". But everybody is forbidden to talk about food.
Then food trucks come by, and everytime a food truck comes by they can all go to the food truck but they have to be sure everybody wants to eat too.
:D (That was fun)
Cristian Reyes
Cristian Reyes
Lesson completed
in response to Scott Cleveland Show comment
All of them only if they are different kind of winning tickets
David Li
David Li
Lesson in progress
in response to Daniël Petri Show comment
Not sure how good of an example this was but it was pretty funny.
Jonathan Bush
Jonathan Bush
Lesson completed
Success in playing chess is not always based solely on reading the board. Sometimes you gain useful information from reading your opponent's emotions. I once read a story about a game Fischer played where his opponent laid a trap in the opening. Fischer was about to walk into the trap, but then noticed his opponent was unusually quiet and withdrawn. This raised his suspicions, and he looked at the position more deeply, thereby discovering the trap. Of course other, more interactive, games such as Poker display this feature more prominently.
Mikael Macial
Lesson in progress
in response to Anthony Falez Show comment
Then you have to predict your enemy's action, knowing he knows what would probaly be your first movement. At the end, it seems more like luck than predicting your enemy's thoughts..