Hid the probability of at most 2 rainfalls by day five and at least 3 raillid Customers arrive at the service counter at the rate of 15 per hour. What is the probability that the arrival time between consecutive customers is less than three minutes? Suppose that the amount of time one spends in a bank is exponentially distributed with mean 15 minutes. (a) What is the probability that a customer will spend more than 20 minutes in the bank? (b) What is the probability that a customer will spend more than 20 minutes in the bank give that he is still in the bank after 6 minutes? ding