SOLUTION: An auto parts manufacturer finds that the useful life of a spark plug in a car is approximately normally distrbuted with a mean of 9 months and a standard deviation of 2.5 months.

Question 276904: An auto parts manufacturer finds that the useful life of a spark plug in a car is approximately normally distrbuted with a mean of 9 months and a standard deviation of 2.5 months. What is the probability that a randomly selected plug will last more than 7 months.
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
An auto parts manufacturer finds that the useful life of a spark plug in a car is approximately normally distrbuted with a mean of 9 months and a standard deviation of 2.5 months. What is the probability that a randomly selected plug will last more than 7 months.
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z(7) = (7-9)/2.5 = 2/2.5 = 0.8
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P(x > 7) = P(z > 0.8) = 0.2119
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Cheers,
Stan H.

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