All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Logic
Prime Perimeter (Posted on 2005-03-11) Difficulty: 3 of 5

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?

See The Solution Submitted by Erik O.    
Rating: 2.8235 (17 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re: solution | Comment 62 of 89 |
(In reply to solution by gary wallravin)

1,5,7 is not a valid combination for sides of a triangle...bcoz to form a triangle, the sum of two sides must be greater than the third this case, 1+5 is not greater than 7 so you cannot form a triangle using this solution would be 5,7, me it makes sense bcoz 11 is a prime number and the perimeter which is 5+7+11=23 is a prime number...and with this combination you can form a triangle bcoz 5+7>11, 7+11>5 and 5+11>7...but i may be wrong of course...
  Posted by em on 2005-03-21 02:20:42

Please log in:
Remember me:
Sign up! | Forgot password

Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (2)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Copyright © 2002 - 2021 by Animus Pactum Consulting. All rights reserved. Privacy Information