Wednesday, August 02, 2017

Green Eyed Dragons

Cool puzzle:

There are a hundred dragons on an island. All of them have green eyes. All of them are supremely rational thinkers. 

Alas, there is a curse on the island where if a dragon learns that it has green eyes, it will turn into a sparrow at the next midnight. Because of this curse, none of the dragons are allowed to talk about eye color and none of them can look at their own reflection. One day a human comes along for a vacation to the island and he has a lot of fun with the dragons.  

The dragons have been living in peace for all eternity. 

When the human leaves, there is a farewell party with all 100 dragons present. Upon departure, the human says: "At least one of you has green eyes".

What are the consequences, if any, of this violation of the Federation's Prime Directive?

Think about it-- since the dragons can see each other's eyes, did the human give them any new information?


  1. L and I think the answer is no change because of no new information. Each dragon would think that the human is referring to the other dragons.

    1. P & L, I came across the problem on this site of interest: Harvard Physics Problem of the Week. (with solutions!). See problem #2.

    2. The answer wasn't as intuitive as we thought.