Radio stations in a certain country use a sequence of 5 or 6 letters as their station identification call letters. The first letter must beZ or K or B . Assume there are no restrictions on the remaining letters, and repetition is allowed.
a) How many 5-letter station identifications are possible?
b) How many 6-letter station identifications are possible?
c) How many total station identifications are possible?
d) The identification for a randomly-chosen radio station is 5 letters in length. What is the probability that all 5 letters are different?
