How many prime numbers are there between 20 and 30 ?
(A) 0
(B) 1
(C) 2
(D) 3
(E) 4
We check each number between 20 and 30 .

None of 20, 22, 24, 26, 28, and 30 is a prime number, because each has a factor of 2.

Neither 21 nor 27 is a prime number, since each has a factor of 3 .

Also, 25 is not a prime number, since it has a factor of 5 .

We do not need to look for any larger prime factors, since this leaves only 23 and 29 , each of which is a prime number. Therefore, there are 2 prime numbers between 20 and 30 .

ANswer: (C)