4.103 A fast-food restaurant located at a commercial area indicates that, on average, it receives 20 orders each morning from 7:00 a.m. to 8:00 a.m. Since this is a rush hour, the restaurant has to prepare food items within 10 minutes of receiving an order. Typically, each order is prepared by a staff member. If any order is not served on time, then the order might be canceled.

a. How many staff members should be hired so that the stall can claim that 90% of the orders will be completed on time?

b. What is the probability that two of the staff members hired for part

(a) would have no orders to prepare for an entire morning?

c. Suppose that the restaurant decides to hire one less member than determined in part (a). What is the probability that customers would cancel their orders at this staffing level?

d. Given the number of staff members hired in part (c), what is the probability that two members would be idle for an entire morning?