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?
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 20051030 09:58:08 