statistics
posted by victor .
According to a bank, the time taken by its customers to use cash dispensing machines is normally distributed with a mean of 18 seconds and a standard deviation of 3 seconds.
I) What is the probability that a customer selected at random takes less than 13 seconds?
II) Find the proportion of customers that take :
a) Between 15 and 21 seconds to use the cash dispensers?
b) Between 12 and 24 seconds to use the cash dispensers?

Z = (scoremean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions related to the Z scores.