February 20, 2017

Homework Help: Statistics

Posted by Toni on Wednesday, September 29, 2010 at 12:45am.

A certain company makes 12-volt car batteries. After many years of product testing, the company knows that the average life of a battery is normally distributed, with a mean of 45 months and a standard deviation of 7 months. If the company does not want to make refunds for more than 10% of its batteries under the full-refund guarantee policy, for how long should the company guarantee the batteries (to the nearest month)?
The choice of answers:
58 months
53 months
36 months
45 months
49 months

*I came out with 45 but was told that was wrong. What did I do wrong. Thanks to those who answer in advance.

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