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?

Does the question mean that B and C know that even A couldn't guess his number by just seeing the numbers on B's and C's forehead ?

Edited on March 12, 2005, 5:14 am

Posted by Sachin on 2005-03-12 05:12:38