Problem
A simple random sample of 100 postal employees is used to test if the average time postal employees have worked for the postal service has changed from the value of 7.5 years recorded 20 years ago. The sample mean was 7 years with a sample standard deviation of 2 years. The hypotheses being tested was whether there was a difference between the sample mean and the mean from 20 years ago.
What is the P-value for the test to show this?