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Topic: Do you know your number now? (Read 1392 times) |
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Noke Lieu
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Do you know your number now?
« on: Feb 29th, 2012, 4:29pm » |
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Alice and Bob each have one of two consecutive positive integers written on their foreheads.
Alice sees Bob’s number, and Bob sees Alice’s number.
Taking turns to ask "Do you know your own number?" is there is a way for them to find out the number on their own forehead?
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towr
wu::riddles Moderator
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Re: Do you know your number now?
« Reply #1 on: Feb 29th, 2012, 10:27pm » |
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Yes, as long as they're perfect logicians and answer the question when they can.
turn 1, if Alice doesn't know it eliminates 2-1
turn 2, if Bob doesn't know it eliminates 1-2 and 2-3
turn 3, if Alice doesn't know it eliminates 3-2 and 4-3
turn 4, if Bob doesn't know it eliminates 3-4 and 4-5
etc
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