Question: A company claims that the rubber belts it manufactures have a mean service life of at least 800 hours with the standard deviation less than 5 hours. A simple random sample of 20 belts is observed:

800, 780, 790, 820, 810, 840, 750, 795, 805, 810, 820, 800, 801, 802, 803, 804, 812, 805, 801, 802. Test the assumption of the company! Assume the normally distributed service life!