A consumer organization wants to estimate the actual tread wear index of a brand name of tires that claims"graded 250" on the sidewall of the tire. A random sample of n=19 indicates a sample mean tread wear index of 235.3 and a sample standard deviation of 23.6. Complete parts(a) through(c).

a.

Assuming that the population of tread wear indexes is normallydistributed, construct a 95% confidence interval estimate of the population mean tread wear index for tires produced by this manufacturer under this brand name.