Before you look up the answer, see if you can figure out this puzzle:
Shown above are four men buried up to their necks in the ground. They cannot move, so they can only look forward. Between A and B is a brick wall which cannot be seen through.
They all know that between them they are wearing four hats--two black and two white--but they do not know what color they are wearing. Each of them know where the other three men are buried.
In order to avoid being shot, one of them must call out to the executioner the color of their hat. If they get it wrong, everyone will be shot. They are not allowed to talk to each other and have 10 minutes to fathom it out.
After one minute, one of them calls out.
Question: Which one of them calls out? Why is he 100% certain of the color of his hat?
There's no trick; just a logical answer -if you can put yourself into these guys' place. Which is, after all, a very bad place to be. Link -via Boing Boing
By the way, the answer to most of these is that the person with the most amount of information cannot be sure of the answer. That added information allows someone with just a bit less information to guess correctly.