Question

which number is not prime? 23 31 2 12

Explanation:

Step1: Recall prime number definition

A prime number is a number greater than 1 that has no positive divisors other than 1 and itself.

Step2: Check 23

23 > 1. Divisors of 23: 1, 23. So 23 is prime.

Step3: Check 31

31 > 1. Divisors of 31: 1, 31. So 31 is prime.

Step4: Check 2

2 > 1. Divisors of 2: 1, 2. So 2 is prime.

Step5: Check 12

12 > 1. Divisors of 12: 1, 2, 3, 4, 6, 12. Since it has divisors other than 1 and itself, 12 is not prime.

Answer:

12 (from the options: the number 12 in the fourth box)