Tennis-Warehouse recently conducted a study of long distance phone calls made by its employees. The study showed that the length of the calls has a mean of 3.2 minutes, a standard deviation of 0.50 minutes and it follows the normal probability distribution.
(a) What portion of the calls was between 3.2 and 4 minutes?
(b) What portion of the calls was more than 4 minutes?
(c) What portion of the calls was between 4 and 4.5 minutes?
(d) What portion of the calls was between 3 and 4.5 minutes?