A report in USA today (July 7, 1995) stated that the average age of commercial jets in the U.S. is 14 years. An executive of a large airline company selects a sample of 40 airplanes and finds that the...

A report in USA today (July 7, 1995) stated that the average age of commercial jets in the U.S. is 14 years. An executive of a large airline company selects a sample of 40 airplanes and finds that the average age of the planes is 11.8 years. The standard deviation of the sample is 2.7 years. Is it true that the average age of the planes in his company is less than the national average? (solve without excel)