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 long-distance calls has changed. Fifty calls, originating from the town, was randomly selected and the following summary minutes.

Σ?=205 Σ(?−?̅)2=56.43

1. a) Calculate the sample mean, ?̅.

1. b) Calculate the sample standard deviation


2. 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.