SOLUTION: A manufacturer of automobile batteries claims that the average length of life for its entire population of Grade A battery is 72 months. However, the full-replacement guarantee on

Question 661107: A manufacturer of automobile batteries claims that the average length of life for its entire population of Grade A battery is 72 months. However, the full-replacement guarantee on this brand is for just 36 months. Suppose the standard deviation of the life length of the population is known to be 14 months and the population distribution for life length is normal. The sales forecast is for 1,000,000 batteries next year.

Approximately what percentage of the 1,000,000 batteries would we expect to fail during their fifth year of life?
Answer by ewatrrr(24785) (Show Source): You can put this solution on YOUR website!

 

Hi,

 mean is 72mo and SD is 14mo

P(x ≤ 60mo)= P((z ≤ (60-72)/14) = P(z ≤ -.8571) = .1957  0r 19.57%  



1,000,000 batteries would we expect to fail during their fifth year of life? 

 only 19.57% of them or 195,700  

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