1 A very small takeaway cafe with 2 baristas has customers arriving at it as a Poisson process of rate 60 per hour. It takes each customer 3 min- utes, on average, to be served, and the service times are exponentially distributed. Interarrival times and service times are all independent of each other. There is room for at most 5 customers in the cafe, includ- ing those in service. Whenever the cafe is full (i.e. has 5 customers in it) arriving customers don't go in and are turned away. Customers leave the cafe immediately upon getting their coffee. Let N(t) be the number of customers in the cafe at time t, including any in service. N(t) is a birth and death process with state-space S = {0, 1, 2, 3, 4, 5}. (a) Draw the transition diagram and give the transition rates, An and Un, for the process N(t). (b) If there is one customer already in the cafe, what is the probability that the current customer gets her coffee before another customer joins the queue?
