An urn contains 15 numbered balls, of which 6 are red and 9 are white. A sample of 5 balls is to be selected.
a) How many different sample are possible? C(15,5)
b) How many samples contain only white balls? C(9,5)
c) How many sample contain 2 red balls and 3 white balls? C(9,2) * C(6,3)
d) How many samples contain at least 2 red balls? C(6,1) * C(9,4) + C(E