Suppose that there is a black urn containing nine black balls and three yellow balls and there is a yellow urn containing six black balls and six yellow balls. An experiment consists of selecting at random a ball from the black urn and then (without replacing the first ball) selecting at random a ball from the urn having the color of the first ball. Required:
a. Construct a tree diagram showing the probabilities associated with this problem. Write a probability on each branch (6 branches).
b. Find the probability that the second ball is yellow.