CWD Business systems maintains a successful Telecom sales department for Top up call credit in which a clerk takes orders by telephone. If the clerk is occupied on one line, incoming phone calls to...

f. What is the probability that a customer will have to wait for service (Pw)?
g What is the probability that there is exactly 2 customers in the system?
h) What is the probability that there are more than 3 customers in the system?

Extracted text: CWD Business systems maintains a successful Telecom sales department for Top up call credit in which a clerk takes orders by telephone. If the clerk is occupied on one line, incoming phone calls to the department are answered automatically by an answering machine and asked to wait. As soon as the clerk is free, the party that has waited the longest is transferred and answered first. Calls come in at a rate of about 15 per hour. The clerk is capable of taking an order in an average of 3 minutes. Calls tend to follow a Poisson distribution, and service times tend to be exponential. The clerk is paid $15 per hour, but because of lost goodwill and sales, CWD loses about $30 per hour of customer time spent waiting for the clerk to take an order.