Problem Solving
If X and Y are prime numbers, which of the following can not be the sum of X and Y? (A) 5 (B) 9 (C) 13 (D) 16 (E) 23 The prime numbers less than 23 are1, 2, 3, 5, 7, 11, 13, 17 and 19. The choices 5,9,13 and 16 can be written as [2+3], [2+7], [2 +11] and [5+11]. It is only 23 which can be the sum of two prime numbers. So, (E) is the answer.
