According to a report from a business intelligence company, smartphone owners are using an average of 19 apps per month. Assume that number of apps used per month by smartphone owners is normally distributed and that the standard deviation is 3.

a. If you select a random sample of 16 smartphone owners, what is the probability that the sample mean is between 18.5 and 19.5 ?

0.485

b. If you select a random sample of 16 smartphone owners, what is the probability that the sample mean is between 18 and 19?

(Round to three decimal places as needed.)