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?

# Mean and standard deviation

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