Question

Of the following numbers , which one os prime : 14,13,21,23

Answer 1

Prime refers to numbers that cannot be divided by any number but themselves and 1.

14 can be eliminated, as it is even (no primes except 2 are even)
13 has no divisors. It is prime.
21 has 4 divisors. It is not prime.
23 has no divisors. It is also prime.

Two numbers of this list are prime; 13 and 23.