What is a 95% confidence interval for , the population mean time the current postal service employees have spent with the postal service?

7 2

7 1.984

7 0.4*

7 0.2

7 0.04

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, as recorded 20 years ago. The sample of the current employees gave a mean service time, 7 years with a standard deviation of s = 2 years. Assume the distribution of the time the employees work in service jobs is approximately normal.

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