The average of all prime numbers between 20 and 40 is

The correct answer is Option (2) → 30

A prime number has no factors other than 1 and itself, and the average is the sum divided by how many numbers there are. The numbers from 21 to 39 are tested for the small factors 2, 3 and 5:

• Primes between 20 and 40: 23, 29, 31, 37 (21, 27, 33, 39 are multiples of 3, 25 and 35 of 5, and the even numbers of 2)

• Sum of the four primes: \(23+29+31+37=120\)

• Average of the four: \(\frac{120}{4}=30\)