A marketing executive decides to limit his company’s ads to three channels. Under consideration are the German networks ARD, ZDF, RTL, SAT1, and PRO 7.

(a) How many combinations of three channels exist for the executive to choose from? List all the possibilities.

(b) The marketing executive wants to run five different commercials five times a day on the three selected channels, with the option of repeating one multiple times. How many possibilities does he have if the order of the commercials does not matter?