Question

You visit a remote desert island inhabited by one hundred very friendly dragons, all of whom have green eyes. They haven't seen a human for many centuries and they are very excited about your visit. They show you around their island and tell you all about their dragon way of life (dragons can talk, of course). They seem to be quite normal, as far as dragons go, but then you find out something rather odd. They have a rule on the island which states that if a dragon ever finds out that he/she has green eyes, then at precisely midnight on the day of this discovery, he/she must relinquish all dragon powers and transform into a long-tailed sparrow. However, there are no mirrors on the island, and they never talk about eye color, so the dragons have been living in blissful ignorance throughout the ages. Upon your departure, all the dragons get together to see you off and in a tearful farewell you thank them for being such hospitable dragons. Then you decide to tell them something that they all already know (for each can see the colors of the eyes of the other dragons). You tell them all that at least one of them has green eyes. Then you leave, not thinking of the consequences (if any). Assuming that the dragons are (of course) infallibly logical, what happens? If something interesting does happen, what exactly is the new information that you gave the dragons?

Answer 1

The rest of the Question Reads:

You tell them all that at least one of them has green eyes. Then you leave, not thinking of the consequences (if any). Assuming that the dragons are (of course) infallibly logical, what happens?

Step-by-step explanation:

Since there are no mirrors, they are unable to tell the color of their own eyes so they must rely on another dragon. If they are as logical as it comes two dragons sitting together will be unable to tell which of them really has green eyes.

Now it seems that there must be three or more dragons present for this to be solved. Imagine that there are Dragons A, B and C. They will look at each other and understand that one of them might have green eyes.

C will look at A and B

B will look at A and C

A will look at B and C

Two of the dragons will wait to see if one of them will transform and if neither of the two does then he will believe himself to have green eyes. At midnight, he will turn a sparrow. When this happens the other dragons that were in the trio will also believe that they have green eyes and will also turn into sparrows.

In conclusion, a group of dragons staring at each other will eventually all believe that they have green eyes and will all turn into sparrows.