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 re(2): full solution as understood by Charlie)

In Charlie's Reply:

Now i get it what youare saying, you mean to say in scenario 1. when C assumes if his number is 3, then He would assume the B can think his numbers to either 3 or 5.

Yes, i think it has gone to next level of complication. I will think about it ans see if I can come with any answer.

Nice problem EriK.

Edited on March 12, 2005, 4:56 am

Posted by Sachin on 2005-03-12 03:06:51