A group of five people want to put a set of locks on a chest and distribute keys to the locks amongst themselves in such a way that all the locks on the chest could be opened only when at least three of them were present to open it.

How many locks would be needed, and how many keys?

Five locks, and five keys. The chest could only be opened when all five people are present (which, in turn, satisfies that at least three of them must be present.

Ah, the old "only if" versus "if and only if" loophole ..

Posted by DJ on 2004-03-03 16:31:15