A person arrives at a certain bus stop each morning. The waiting time, in minutes, for a bus to arrive is uniformly distributed on the interval (0, 15).
a. Find the mean waiting time.
b. Find the standard deviation of the waiting times.
c. Find the probability that the waiting time is between 5 and 11 minutes.
d. Suppose that waiting times on different mornings are independent. What is the probability that the waiting time is less than 5 minutes on exactly 4 of 10 mornings?