What is the average of the first 10 prime numbers?

Correct answer: 12.9. The first 10 primes are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29. Their sum is 129, so the average is 129 ÷ 10 = 12.9.

Background: A prime number has exactly two factors: 1 and itself.

• 12.5: 12.5 is not 129 ÷ 10.
• 2.6: 2.6 is not 129 ÷ 10.
• 13.2: 13.2 is not 129 ÷ 10.

Did you know? 2 is the only even prime number.

Memory trick: Sum 129 ÷ 10 = 12.9.