A pizza restaurant claims that its mean delivery time is 30 minutes. An independent company times a randomly selected delivery, which takes 40 minutes.
a. Assuming the delivery times are approximately normally distributed with mean 30 minutes and standard deviation 4 minutes, find the probability that a randomly selected de- livery would take at least 40 minutes.
b. If the assumptions you made in part (a) are true, is the 40-minute delivery an unusual event?
c. Describe a scenario in which the 40-minute delivery is not an unusual event.
d. On the basis of the 40-minute delivery, do the assumptions you made in part (a) seem reasonable? Should a more thorough investigation occur?