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. In serving themselves, customers take about 15 seconds, exponentially distributed.
What percentage of the time is the urn being used?
What is the probability that that three or more people are in the cafeteria getting coffee?
If the cafeteria installs an automatic vendor that dispenses a cup of coffee at a constant time of 15 seconds?