Which of the following is a composite number?

A. 31

B. 63

C. 61

D. 13

A composite number is an integer that is NOT prime.

Here is a trick: if you add the digits of a number and this sum divides by 3, the number is divisible by 3:

so B) 63

6+3=9

which is divisible by 3, and so is 63: this is a composite number

The answer is b b is composite