Roosevelt University's 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.

1. How many customers would you expect to see on the average at the coffee urn?

2. How long would you expect it to take to get a cup of coffee?

3. What percentage of time is the urn being used?

4. What is the probability that three or more people are in the

cafeteria?