Bright Side - The picture shows four men. two of them wear black hats, two wear white. they don't know what color of hat they wear. they stand one after another in
The Answer To The Black And White Hat Puzzle : Who Will Shout First ? - YouTube
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Four hats
A Mathematician Says Most People Can't Solve the '3 Hats' Puzzle
Another hats and prisoners puzzle
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Open Source For Geeks: Four men in hats puzzle
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logic
Men with hats riddle - AngelCom
A Mathematician Says Most People Can't Solve the '3 Hats' Puzzle
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Induction puzzles - Wikipedia
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Answer to Riddle #12: Three Men and Red & Blue Hats