I have a bag containing the digits 0 through 9, and used six of them to stick two different three-digit perfect squares on the foreheads of Paul and George. Both Paul and George know this fact, but each one can see only the other's number.

I ask Paul, "How many of the digits remaining in my bag can you exactly tell me?"

Paul replies, "Three."

If I now ask the same question to George, what should he reply?

(In reply to George's answer by Bob Smith)

So that actually means he only knows 3: the fourth might be either a 1 or a 7.  He doesn't know all 4.

Posted by Charlie on 2005-08-04 18:05:10