Monday, September 12, 2005
Really Tough Brain Teaser
Okay, this is a tough one. Or maybe it's not so tough, but it took me a long time to figure it out, and I needed a hint.
Mike shows nine playing cards (5 Diamonds; 2 Hearts; and 2 Clubs) to 5 logicians. Mike then blindfolds the logicians and tapes the 5 Diamonds cards to their foreheads. He hides the other cards, then removes the blindfolds. Mike then asks the logicians what suit of card they have on their forehead. After a few minutes, one logician blurts out that he knows he has a Diamond taped to his forehead. How does he know?
Good Luck! I've put three levels of hints in the comments to this post.
Mike shows nine playing cards (5 Diamonds; 2 Hearts; and 2 Clubs) to 5 logicians. Mike then blindfolds the logicians and tapes the 5 Diamonds cards to their foreheads. He hides the other cards, then removes the blindfolds. Mike then asks the logicians what suit of card they have on their forehead. After a few minutes, one logician blurts out that he knows he has a Diamond taped to his forehead. How does he know?
Good Luck! I've put three levels of hints in the comments to this post.
# posted by eric @ 1:15 PM 
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HINT NUMBER TWO: Each one of them is trying to work out the answer, and the one who answers bases his answer on the others' failure to answer.
HINT NUMBER THREE: If the five logicians were assigned as follows: 1 diamond, 2 hearts, 2 clubs, then the guy with the diamond would obviously be able to figure out his card. If they were assigned as follows: diamond, diamond, heart, club, club, then the second guy would be able to know he was a diamond based on the first guy's failure to answer. Go from there...
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