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Test Tires Using a 95% Confidence Interval of Average Mileage

"Joe" is he shop manager at a truck line and is approached by a salesman about some new tires. The salesman assures Joe that the tires will get an average of 60,000 miles before wearing out.

Not being that gullible Joe asks for 100 tires for a test. The tires are mounted and run to wear-out and the 95% confidence interval of average mileage is calculated.

Average 61,000
Confidence interval 58.000 miles to 64,000 miles

What number or numbers might the salesman point to? What number or numbers might Joe be concerned about? What is the "correct" number? (and this is a "trick" question!)

Assume the sample mean and confidence interval was:
Average 63,000
Confidence interval 60,000 to 66,000

Why might Joe still be concerned?

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What number or numbers might the salesman point to? What number or numbers might Joe be concerned about? What is the "correct" number? (and this is a "trick" ...

Solution Summary

This solution determines whether a shop manager should invest in a line of new tires based on a statistic test to determine the average number of miles a tire can endure before wearing out.

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