There are 12 fathers and 15 mothers who have offered to chaperone a school trip. 6 of these parents are chosen at random. a.What is the probability

 There are 12 fathers and 15 mothers who have offered to chaperone a school trip. 6 of these parents are chosen at random.

a.    What is the probability that exactly 3 of these are mothers?

b.    What is the probability that at least 2 of the mothers are chosen?