What number between 20 and 25 is a prime number?

Prime numbers are numbers that have only one factor pair; 1 and themselves.

Let's start from 21.

21 = 1 x 21, 3  x 7.
This has two factor pairs, this is not prime.

Let's try 22.

22 = 1 x 22, 2 x 11.
This also has two factor pairs, this is not prime.

Let's try 23.

1 x 23.
This is a prime number, as it only has one factor pair; 1 and itself.

23 is your prime number.

I hope this helps!

23 is a prime number because the only multiplacation is 1 times 23