Question

what is the probability that a number selected at random from the set {2,3,7,12,15,22,72,108} will be divisible by both 2 and 3?

Answer 1

First, look at how many numbers are divisible by 2 and 3. 
12,72, and 108 and are all divisible by both 2 and 3. That makes 3 out of 8 numbers.
Depending on what form you have to put the probability, that makes it 3:8, 3 out of 8, or 37.5% probability.