You and two other people have numbers written on your foreheads. You are all told that the three numbers are primes and that they form the sides of a triangle with a prime perimeter. You see 5 and 7 on the other two heads and both of the other people agree that they cannot deduce the number on their own foreheads.

What is the number written on your forehead?

(In reply to Trying to solve this... by Tristan)

Tristan,

In your words, "I don't agree with pcbouhid's solution, but I didn't look long enough to be sure".

I think you have only one thing to do:  look at it long enough, discover a possible error in my reasoning, and only after this, you can say "I don't agree, BECAUSE..."

It's too easy to say "I didn't agree", but you have to put in the paper WHY you don't agree, not saying "I didn't look long enough".

Posted by pcbouhid on 2005-03-13 21:07:54