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The undiscovered numbers (Posted on 2005-10-29) Difficulty: 3 of 5
Arthur and Bert each writes down a positive integer on a piece of paper and then shows it to Charles. Charles then writes two numbers on a blackboard, visible to Arthur and Bert: one of them is the sum of Arthur's and Bert's numbers, and the other is a random number.

After this Charles asks Arthur if he knows Bert's number. If Arthur says he doesn't know, then he asks Bert if he knows Arthur's number. If Bert says he doesn't know, Charles continues with Arthur, then if necessary with Bert and so on... until he gets a positive answer.

When will Charles get a positive answer?

See The Solution Submitted by Hugo    
Rating: 3.6667 (6 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
guesses? | Comment 3 of 32 |
I didn't realize that Arthur is allowed to guess Bert's number (and vice versa).  The problem, as I read it, has 'C' alternately asking 'A' and 'B' if they know the other guy's number, not that they then get to guess and thus learn the truth.
  Posted by Larry on 2005-10-30 09:58:08
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