A local tire retailer has determined that his XL100 tire has a mean lifetime of

Question

A local tire retailer has determined that his XL100 tire has a mean lifetime of 70,000 miles. Over the years, he has found that the lifetime of the tire actually follows a normal distribution with a standard deviation of 12,000 miles. Based upon his analysis a. What percent of the tires will last less than 50,000 miles? _____ b. What percent of tires will last more than 80,000 miles? ______ c. What percent of tires will last between 62,000 miles and 82,000 miles? _____ d. Ten percent of the tires will last more than what number of miles? ____

Explanation / Answer

a. normalcdf(0,80000,70000,12000) = 0.7977 b. normalcdf(80000,99999999999,70000,12000) = 0.2023 c. normalcdf(62000,82000,70000,12000) = 0.5889 d. invNorm(0.90,70000,12000) = 85379

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