An urn contains white balls numbered 1 to 15 and black balls also numbered 1 to 15. Suppose you draw 4 balls. What is the probability that (b) you get exactly one pair with the same number? (c) you get two pair with the same numbers?

Question

anonymous · Answer

First of all, what the total number of ways to draw the four balls?

anonymous · Answer

b shouldn't be that hard

anonymous · Answer

c is easier.

anonymous · Answer

yeah i'll do c
(15C2) / (30C4) 

:DD

anonymous · Answer

got b yet?

anonymous · Answer

b) C(15,1) C(14,2) C(2,2) (2*2) / (30C4)