In 2015, the average duration of long-distance telephone calls from a certain town was 3.9 minutes. A telephone company wants to perform a test to determine whether this average duration of...

In 2015, the average duration of long-distance telephone calls from a certain town was 3.9 minutes.

A telephone company wants to perform a test to determine whether this average duration of longdistance calls has changed. Fifty calls, originating from the town, was randomly selected and the

following summary minutes.

∑ ? = 205 ∑(? − ?̅)
2 = 56.43

a) Calculate the sample mean, ?̅.
b) Calculate the sample standard deviation

c) Using the p value approach at the 1% level of significance, test whether the mean duration of

long-distance calls from the town had increased.