Question

A population consists of 15 items, 10 of which are acceptable. in a sample of 4 items, what is the probability that exactly 3 are acceptable?

Answer 1

# of ways to pick 3 "acceptable": 10C3 = 120
# of ways to pick 1 not acceptable: 5C1 = 5
# of ways to pick 4 where exactly 3 are acceptable: 120*5 = 600
# of ways to pick 4 with no restrictions: 15C4 = 1365