In the past the average length of an outgoing telephone call from a business office has been 146 seconds. A manager wishes to check whether that average has decreased after the introduction of policy...

In the past the average length of an outgoing telephone call from a business office has been 146 seconds. A manager wishes to check whether that average has decreased after the introduction of policy changes. A sample of 100 telephone calls produced a mean of 143 seconds, with a standard deviation of 28 seconds

Perform the relevant test at the 0.05 level of significance