A cafeteria serving line has a coffee urn (like a system) from which customers serve themselves. Arrivals at the urn follow a Poisson distribution at the rate of 3 per minute. In serving themselves, customers take about 15 seconds, exponentially distributed. (a) How many customers would you expect to see, on average, at the coffee urn? (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 3 or more people are in the cafeteria?
