Question

billy is thinking of three numbers from 1 through 9 with a sum of 17. each number is used only once. What are the numbers?

Answer 1

This is very interesting.

Billy could be thinking of

1, 7, and 9
2, 6, and 9
2, 7, and 8
3, 5, and 9
3, 6, and 8
4, 5, and 8
or
4, 6, and 7

but no other set of three numbers.