Statistics 十萭火急請幫助

2008-02-13 6:40 am

A tire company has developed a new type of steel-belted radial tire. Extensive testing indicates the population of mileages obtained by all tires of this new type is normally distributed with a mean of 40,000 miles and a standard deviation of 4,000 miles. The company wishes to offer a guarantee providing a discount on a new set of tires if the original tires purchased do not exceed the mileage stated in the guarantee.

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What should the guaranteed mileage be if the tire company desires that no more than 2 percent of the tires will fail to meet the guaranteed mileage?

回答 (1)

Tenkarai

2008-02-16 6:56 am

✔ 最佳答案

For z-distribution, accumulative percentage up to 98% is about 2.053 SD. You can also check the table at the back of your textbook for another number. It should be around 2.06 SD.

Cause we are working on the other end of the normal curve, we need to minus the SD from the mean:

Mean - 2.053(SD)
= 40000 miles - 2.053(4000 miles)
= 31788 miles

So... it means on average about 2% of the tires may not make it to 31788 miles, and it should be your proposed guaranteed mileage.

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Statistics 十萭火急 請幫助

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Statistics 十萭火急請幫助