The Judy Gray Income Tax Service is analyzing its customer service operations during the month prior to the April filing deadline. On the basis of past data it has been estimated that customers arrive according to a Poisson process with an average inter arrival time of 12 minutes.

The time to complete a return for a customer is exponentially distributed with a mean of 10 minutes. Based on this information, answer the following questions:

a. If you went to Judy, how much time would you allow for getting your return done?

b. On average, how much room should be allowed for the waiting area?

c. If Judy stayed in the office 12 hours per day, how many hours on average, per day, would she be busy?

d. What is the probability that the system is idle?