SOLUTION: The lifetime of a certain manufacturer's washing machine is normally distributed with mean 4 years. Only 15 percent of all these washing machines last at least 5 years. What is the

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Question 654024: The lifetime of a certain manufacturer's washing machine is normally distributed with mean 4 years. Only 15 percent of all these washing machines last at least 5 years. What is the standard deviation of the lifetime of a washing machine made by this manufacturer?
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Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
The lifetime of a certain manufacturer's washing machine is normally distributed with mean 4 years. Only 15 percent of all these washing machines last at least 5 years. What is the standard deviation of the lifetime of a washing machine made by this manufacturer?
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Find the z-value with a right tail of 15%: invnorm(0.85) = 1.0364
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Solve for standard deviation using x = z*s + u
5 = 1.0364*s + 4
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1.0364*s = 1
s = 0.9648
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Cheers,
Stan H.