Question:The records of the 100 postal employees at a postal station in a large city showed that the average time these employees had worked for the...

Question:The records of the 100 postal employees at a postal station in a large city showed that the average time these employees had worked for the postal service was = 9 years. Assume that we know that the standard deviation of the population of times U.S. postal service employees have spent with the postal service is approximately Normal, with standard deviation ? = 5 years. A 95% confidence interval for the mean time ? the population of U.S. postal service employees have spent with the postal service is

· 9 ± 0.82. Incorrect

· 9 ± 0.98. Incorrect

· 9 ± 9.80. Incorrect

· not trustworthy. (True Answer )Correct

If the answer is the last one" not trustworthy", please explain in detail. Do not just tell me"the conditions of this inference procedure have not been met." I want to know the conditions of this inference procedure have not been met because it's not the SRS or n<15 or...etc??Thank you~~