A telephone-order sales company must determine how many telephone operators are needed to staff the phones during the 9-to-5 shift. It is estimated that an average of 480 calls are received during this time period and that the average call lasts for six minutes. There is no queueing. If a customer calls and all operators are busy, this customer receives a busy sig- nal and must hang up. If the company wants to have at most one chance in 100 of a caller receiving a busy signal, how many operators should be hired for the 9-to-5 shift? Assume arrival rates and service rates are Poisson distributed.