Q3. Supermarkets usually become busy at about 5 p.m. on weekdays, because many workers stop by on the way home to shop. Suppose at that time arrivals at a supermarket's express checkout station are Poisson distributed, with an average of 0.8 people/minute. (6 marks) a. If the clerk has just checked out the last person in line, what is the probability that at least 1 minute will elapse before the next customer arrives? b. Suppose the clerk wants to go to the manager's office to ask a quick question and needs 2.5 minutes to do so. What is the probability that the clerk will get back before the next customer arrives?