Question

What is the mystery number? It is less then 40. You say its name when you start at 3 and count by 3s.You say its name when you start at 5 and count by 5s. It is not 15.

Answer 1

The number must be 30.

Explanation:

The mystery number is less then 40.

You say its name when you start at 3 and count by 3s. This means that it is a multiple of 3.

You say its name when you start at 5 and count by 5s. This means that it is a multiple of 5.

The only two numbers that are multiples of 3 and 5 and less than 40 are 15 and 30.

Since we have been told that the number is not 15, the number must be 30.