In a large department store a customer complaints office handles an average of six complaints per hour about the quality of service.
(a) What is the probability that in any hour exactly six complaints will be received?
(b) What is the probability that in any hour at most six complaints will be received?
(c) What is the probability that more than 20 minutes will elapse between successive complaints?
(d) What is the probability that fewer than 5 minutes will elapse between successive complaints?