Each of four friends orders a sweatshirt from a catalog. There are 15 colors of sweatshirts, 5 of which are all cotton and 10 of which are a blend. Each one orders a different color (no repeats) at random. What is the probability that the friends order only cotton sweatshirts?

Each of four friends orders a sweatshirt from a catalog. There are 15 colors of sweatshirts, 5 of which are all cotton and 10 of which are a blend. Each one orders a different color (no repeats) at random. What is the probability that the friends order only cotton sweatshirts?

a.11/5

b.1/5

c.12/65

d.1/273

the probability is to select 4 cotton sweatshirts out of 15 sweatshirts, the way to select 4 cotton sweatshirts is

4C5 = 5, pick up 4 sweatshirts randomly from 15 sweatshirts is 4C15, thus the probability is