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): Semi-Solution? by Richard)

if so then it has to be 11

Posted by Sachin on 2005-03-11 19:17:15