(a) An urn contains n blue balls and m yellow balls. The balls are withdrawn one at a time until only those of the same colour are left. Find the probability of the event that all balls left are yellow. Verify your answer.

(b) A fish tank contains 3 red, 4 blue, and 2 orange coloured fish. Suppose that the fish are removed randomly from the tank one at a time. What is the probability of the event that the red fish are the first to be removed from the tank completely?