Question 855162
The hard drive reader head is the only likely component to fail, and all that fail are replaced.  These have life expectancy that follows a normal distribution with mean 60 months and standard deviation of 2 months. what is the longest time that the manufacturer can guarantee the hard drives if they want to replace no more than 4% of them?
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Find the z-value with a left-tail of 4%:: invNorm(0.04) = -1.7507
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Find the corresponding time.
x = z*s+u
x = -1.7507*2+60 = 56.49
Ans:: 56 months
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Cheers,
Stan H.