How many non-empty subsets of {1, 2, 3, 4, 5} consist entirely of prime numbers? (We form a subset of the group of numbers by choosing some number of them, without regard to order. So, {1, 2, 3} is the same as {3, 1, 2}.)

The prime numbers are 2, 3, and 5.

Sets with one number: 3choose1=3

Sets with two numbers: 3choose2=3

Sets with three numbers: 3choose3=1

Total: 7

:D

Good job, Aven John!