Saturday, March 28, 2009

N cooperative girls wearing an Hat

This is a classical and instructive puzzle. In a room there are N girls who wear either a Red or Black hat. The color is decided by tossing a coin.

Each girl cannot see her own hat, but she can only see hats worn by other girls. Girls cannot communicate each other. The team wins if at least one of them guesses correctly, and none of them guesses incorrectly. What is the team's best strategy? (In other words, who should talk and who should say in silence?)

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