The amount of time you use on your cell phone each month is approximately normally distributed with a mean of 623 minutes and a standard deviation of 24 minutes.
a. What is the probability that you will talk more than 700 minutes (when the extra charges apply) next month?
b. What range of talk-times represents the middle 50% of the times you will talk?
c. How many monthly bills do you expect to receive until you get the 6th one with extra charges (talk more than 700 minutes)?