Response to the following problem:
Circle J convenience store has two check-out counters. Customers arrive according to a Poisson process at an average rate of one every 90 seconds. On the average, each of the 2 checkers serves 50 customers per hour, and service times follow an exponential distribution. Circle J is considering eliminating one of the 2 checkout counters and having the 2 employees work together, one ringing up the merchandise, the other bagging it.
How fast would their combined average service time have to be if the average time a customer spends in the store is to remain unchanged?