SOLUTION: *please help me solve this: Quality-control studies for Speedy Jet computer printers show that the lifetime of the printer follows a normal distribution with mean 4 years and stan

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Question 1074392: *please help me solve this:
Quality-control studies for Speedy Jet computer printers show that the lifetime of the printer follows a normal distribution with mean 4 years and standard deviation 0.78 years. The company will replace any printer that fails during the guarantee period. How long should Speedy Jet printers be guaranteed if the company wishes to replace no more than 10% of the printers?
Z=_______
X=_______
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
Quality-control studies for Speedy Jet computer printers show that the lifetime of the printer follows a normal distribution with mean 4 years and standard deviation 0.78 years. The company will replace any printer that fails during the guarantee period. How long should Speedy Jet printers be guaranteed if the company wishes to replace no more than 10% of the printers?
Find the z-value with a left tail of 10%
Z=invNorm(0.10) = -1.2816
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Comment:: The time value you want is 1.2816 standard deviations
below the mean
X = -1.2816*0.78 + 4 = 3 years
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Cheers,
Stan H.
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