Three men are sentenced to death, but the judge is in a playful mood.
The men are shown five hats - three black and two white. The men are blindfolded, each has a hat placed on his head, they are tied in position so they can't move, and the blindfolds are removed. The first man can see both others. The second can only see the third. And the third can't see either of the other men. The unused hats have been hidden.
They are told that if any of them can say what colour hat they are wearing, they can all go free. But one incorrect answer means they are all dead men.
The first man says that he does not know.
The second man says that he does not know either.
The third man says that he does know.
How does he know, and what colour is his hat?
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Answer at 9.00 on Monday