please tell me if model one follows M/M/s queue model or M/G/s queue model

please reason which one, i think there is a typo in model service time, since they state exponential disttibution, but why give a standarf deviation???since M/M/s model doesnt need standatf deviation lile M/G/s does???

is my reasoning in fact correct?

please help

The problem at hand relates to a waiting time management of queues in a typical bank. In a bid to improve the level of service at the tellers, a bank manager seeks to find strategies to employ for better service offering that will improve customer satisfaction. The manager is prepared to employ up to 5 cashiers, but not less than 1 . The main management objectives are (i) To have a average customer to wait less than 2 minutes for service, and (ii) the average length of the queue (waiting line) to be 2 persons or fewer. The manager tests several models to help in the decision process. Model 1 Suppose the manager makes the following assumptions: - The distribution of the length of time it takes the cashiers to carry out a service is exponential, with mean 2 minutes and standard deviation of 1.25 minutes; - There is no limit to the queue length during business hours as the bank has a large floor area; - Customers arrive is a Poisson distribution, with mean of 25 per hour - Service is done on a first come first serve basis