Question

A consumer organization wants to estimate the actual tread wear index of a brand name of tires that claims​ "graded

150​" on the sidewall of the tire. A random sample of n=21 indicates a sample mean tread wear index of 137.3

and a sample standard deviation of 24.3.

a.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.

Answer 1

given data are:-

sample size (n ) = 21

sample mean () = 137.3

sampel sd (s) = 24.3

df =(n-1) = (21-1) = 20

t critical value for 90% confidence interval, df = 20 ,both tailed test be:-

[ using t distribution table]

the 90% confidence interval estimate of the population mean tread wear index for tires produced by this manufacturer under this brand name is:-

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