5 There are 5 students and one keg of beer at a wild and crazy campus party. The time to draw a glass of beer follows an exponential distribution, with an average time of 2 minutes. The time to drink a beer also follows an exponential distribution, with a mean of 18 minutes. After finishing a beer, each student immediately goes back to get another beer.

a On the average, how long does a student wait in line for a beer?

b What fraction of the time is the keg not in use?

c If the keg holds 500 glasses of beer, how long, on the average, will it take to finish the keg?