The user-friendly version of this content is available here.
The following content is copyright (c) 2009-2013 by Goods of the Mind, LLC.
This problem trains for: SAT-I.
If the digits a and b of a two-digit number n satisfy a+b is prime, which one of the following choices cannot be the number n:
Adding the digits of each of the choices gives:
and only the second choice is not prime.