A jar contains six red marbles, four green marbles and five yellow ones.

Question

a) determine the number of ways in which any thee marbles can be selected?

b) Determine the number of ways to select four marbles where two are red and two are yellow?

c) Determine the number of ways in which six marbles can be selected where two are red two are green and two are yellow?

so for question a i came up with
p(15,3) = 455

for question b i was thinking
p(4,2) x p (4,2)

and for c
p(6,2) x p(6,2) x (p(6,2)

not sure if those are close though.