A box contains 4 white balls and 5 red balls. I draw 3 of them out of the box, one at a time, and set them aside. What is the probability that the balls I draw alternate between the two colors?
We have two scenarios
White, Red, White = 4/9 * 5/8 * 3/7 = 60/504 ....and...
Red, White, Red = 5/9 * 4/8 * 4/7 = 80 / 504
Adding the probabilities we have [ 60 + 80 ] / 504 = 140/504 = 5/18
