Posted by Nicole on .
A box contains 2 white calls and 7 pink balls. Two balls are drawn at random from the box.
a) If the first ball is drawn and not replaced, what is the probability that two balls will be drawn of different colors?
b) If the first ball is drawn and then put back, what is the probability that two balls will be drawn of different colors?

Math 
Reiny,
P(WP) = (2/9)(7/8) = 7/36
P(PW) = (7/9)(2/*) = 7/36
Prob of your event = 7/36+7/36 = 7/18
if ball is replaced,
Prob(your event) = 2(2/9)(7/9) = 28/81