Fast-food restaurants spend quite a bit of time studying the amount of time cars spend in their drive-throughs. Certainly, the faster the cars get through the drive-through, the more the opportunity for making money. QSR Magazine studied drive-through times for fast-food restaurants and found Wendy’s had the best time, with a mean time spent in the drive-through of 138.5 seconds. Assuming drive-through times are normally distributed with a standard deviation of 29 seconds, answer the following.
(a) What is the probability that a randomly selected car will get through Wendy’s drive-through in less than 100 seconds?
(b) What is the probability that a randomly selected car will spend more than 160 seconds in Wendy’s drive-through?
(c) What proportion of cars spend between 2 and 3 minutes in Wendy’s drive-through?
(d) Would it be unusual for a car to spend more than 3 minutes in Wendy’s drive-through? Why?