Question

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 equals 15 indicates a sample mean tread wear index of 242.9 and a sample standard deviation of 18.3. Complete parts​ (a) through​ (c).

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

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

a. ​No, because a grade of 250 is not in the interval.

b. ​Yes, because a grade of 250 is in the interval.

c. Yes comma because a grade of 250 is not in the interval.

d. No comma because a grade of 250 is in the interval.

C.Explain why an observed tread wear index of 254 for a particular tire is not​ unusual, even though it is outside the confidence interval developed in​ (a).

a. It is not unusual because it is only 0.61 standard deviations above the sample mean.

b. It is not unusual because it is only 0.05 standard deviations above the confidence interval.

c. It is not unusual because it is actually in the confidence interval.

d. It is not unusual because it is just outside the confidence interval.

Answer 1