Question

Which number is prime? A. 57 B. 63 C. 51 D. 59

Answer 1

It's D. 59, because all of the other numbers are divisible by 3, and you can tell by adding up the digits. (5 + 7 = 12, 3 × 4 = 12) (6 + 3 = 9, 3 × 3 = 9) (5 + 1 = 6, 3 × 2 = 6)

Answer 2

D. 59 is the answer