You have been given 10 bags of pearls. You are told that one of the bags is full of those cheap plastic kind of pearls, but the other nine are the real deal. Naturally, you cannot tell the difference just by looking. However, you know that the fake pearls weigh 9 grams each, while the real ones are one gram heavier and weigh 10.

Armed with a very presice scale, you could weigh a pearl from each bag until you find the fake one by weight, but that would take up to 10 weighings. Can you do it in less?

(In reply to Question of a question by Nick Reed)

a) Usually a puzzle like this will say that there are 100 (or some other sufficiently high number that we don't have to worry about running out of pearls (or marbles, or socks, etc. But it might make for an interesting puzzle if we were more limited.

b) as you take the pearls out of each bag, you place them in a separate baggie so that you can return them to their proper bag.

Posted by TomM on 2002-10-08 18:33:44