The time spent on a cell phone is normally distributed, with mean 7 and standard deviation 1.8 minutes.

The time spent on a cell phone is normally distributed, with mean 7 and standard deviation 1.8 minutes. if select a random sample  of 20 phone calls,what is the probability the probality that the sample mean is between 6.8 and 7.2 minutes? if you select a random sample of 150 phone calls, what is the probality that the sample mean is between 6.8 and 7.2 minutes?