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                                               Puzzle
    From a group of three black hats and two white hats, three hats are chosen at random and placed on the heads of three very, very wise men.  The men cannot see the color of their own hats -- in fact, one of the men cannot see at all --he is blind.
    Each man is asked, in turn.
    "What is the color of your hat?"
    The first man looks carefully at the hats of the other two men and says, "I don't know."  He is, of course, very wise , and he is quite right; he can't determine the color of his hat.
    The second man also answers the question "I can't know."  He, also a very wise man, is also right.
    The third man -- the blind man -- is quick to answer when he is asked.  He says, "My hat is black." and he is correct.  How does he know?

 

                                        Answer to the Puzzle
    The first wise man looked at the other two wise men's hats.  If he had seen two white hats, he would have known that his own hat was black, for there are only two white hats.  The first man  did not see two white hats, so he said he didn't know the color of his own hat.
    The second wise man realized that the first had not seen two white hats.  He looked at the third man's hat.  If the third man had had a white hat, the second man would immediately have known that his own hat could not be white, too.  But he said that he didn't know the color of his own hat, so he must have seen a black hat on the head of the third man.
    The third wise man -- the blind one --then knew that his own hat was black, and said so.

 

For reference 参考:

BBC: Funny Logic 逻辑的乐趣

 

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