The secretary at a computers company is pregnant! It may have been one of the three partners' fault, or maybe someone else's. If a partner was the guilty party, he knows it... but he doesn't want the others to know it was him.
The three partners agree that they must know whether it was one of them who made the girl pregnant (thus possibly allowing a suit against the company) or if it was someone else.
How can they decide if one of them is to blame, without anybody having to accept being the father, if that was the case?
(Some notes: They might just write on papers either "I DID IT" or "I WASN'T IT", but the handwriting might give the guilty party away. Putting a white or black marble in an urn (white=innocent, black=guilty) might work, but someone could possibly see what color was being put in; also, if the guilty one went first, the second could peek inside and realize the answer. The optimum solution should not require much --or any-- extra equipment, and should "resist" inquisitive partners. And, of course, being all of them quite capable hackers, computers are out of the question!)
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Submitted by Federico Kereki
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Rating: 4.0000 (8 votes)
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Solution:
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Call the partners A, B and C. Each one thinks of a integer number, and shows it to the next partner. (Thus, A shows his number to B, B shows his to C, and C shows his to A.)
After this, each partner sums his own number and the number that was shown to him, and calls out "EVEN" or "ODD" depending on the sum... but if a partner was the father, he is to lie.
If no one was the father, there should be an even number of "ODD" answers, but if one lied, there will be an odd number of such answers... but no one will be able to deduce who was the father!
A second, simpler, solution [similar to the one posted by e.g.] is: each tosses a coin, and shows it to the next partner, who must either say "SAME" (if it is the same as his) or "DIFFERENT". Once again, the guilty party is to lie. In this variant, if there is a even quantity of "DIFFERENT", nobody is guilty, but if the quantity is odd, someone is the father. |
