Question

Matthew writes a list of all three-digit squares backwards. For example, in his list Matthew writes the three-digit square '625' as '526'. Norma looks at Matthew's list and notices that some of the numbers are prime numbers. What is the mean of those prime numbers in Matthew's list?

Answer 1

447

Explanation:

You want the mean of the prime numbers in the list of digit-reversed 3-digit squares.

Squares

Three-digit squares range from 10² = 100 to 31² = 961. Reversing the digits of these 22 numbers gives a list that includes 3 primes: 691, 163, and 487.

The mean of these primes is ...

(691 +163 +487)/3 = 447

The mean of Norma's list is 447.

<95141404393>