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 246.5 and a sample standard deviation of 22.5.

a.	Assuming that the population of tread wear indexes is normally distributed, construct a 90% confidence interval estimate of the population mean tread wear index for tires produced by this manufacturer under this brand name.

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(Round to two decimal places as needed.)