statistics
posted by nounou .
The time it takes to give a man a shampoo and haircut is normally distributed with a mean of 22 minutes and standard deviation of 3 minutes. Customers are scheduled every 30 minutes. (a) What is the probability that a male customer will take longer than the allocated time? *(b) If three customers are scheduled sequentially on the half hour, what is the probability that all three will be finished withintheir allocated halfhours time?

http://davidmlane.com/hyperstat/z_table.html
set your mean and standard deviation on the graph, then calculate the area below 30, that is the probability of getting a customer done. Cube it for three customers sequentially.