The average waiting time at a drive-in window of a local bank is 10.3 minutes, with a

Question:

The average waiting time at a drive-in window of a local bank is 10.3 minutes, with a standard deviation of 2.7 minutes. Assume the variable is normally distributed. If a customer arrives at the bank, find the probability that the customer will have to wait
a. Between 4 and 9 minutes
b. Less than 5 minutes or more than 10 minutes
c. How might a customer estimate his or her approximate waiting time?