A cafeteria serving line has a coffee urn from which customers serve themselves Arrivals at the urn follow a Poisson distribution at the rate of three per minute. Customer service times are exponentially distributed with a mean of 15 seconds.

a) How many customers on average would you expect to see at the coffee station?

b) How long would you expect it to take to get a cup of coffee?

c) What percentage of time is the urn being used?

d) What is the probability that there are three or more people at the coffee station?