The U. S. Department of Transportation requires tire manufacturers to provide performance information on tire sidewalls to help prospective buyers make their purchasing decisions. One very important piece of information is the tread wear index, which indicates the tire’s resistance to tread wear. A tire with a grade of 200 should last twice as long, on average, as a tire with a grade of 100.

A consumer organization wants to test the actual tread wear index of a brand name of tires that claims “graded 200” on the sidewall of the tire. A random sample of n = 18 indicates a sample mean tread wear index of 195.3 and a sample standard deviation of 21.4.

a. Is there evidence that the population mean tread wear index is different from 200? (Use a 0.05 level of significance.)

b. Determine the p- value and interpret its meaning.