Suppose we are interested in estimating the average number of customers in the supermarket during the morning hours, say, from 9am-11am. We collected the following information: On average, there are 15 customers entering the supermarket in every 5 minutes during that time. On average, a typical customer spent about 20 minutes in the supermarket (from entering to exiting the supermarket). About 20% of customers leave the supermarket without buying anything and the other 80% will go through the checkout area. For those who need to pay, on average, a customer spends about for 5 minutes in the checkout area