A box contains 4 white b***s and 5 red b***s. I draw 3 of them out of the box, one at a time, without replacement. What is the probability that the b***s I draw alternate between the two colors?
The possible draws are
W R W = (4/9)(5/8)(3/7) = 5/42 and
R W R = (5/9) (4/8) (4/7) = 10/63
And the sum of these =
5/42 + 10/63 =
5/18
