The lifetime is months is 85.24 months
Step-by-step explanation:
In this question you are supposed to find the months "X' that is exceeded by 10% of the hard drives.
Exceeded by 10% means a value X on the frequency distribution table that is to the right of the mean score of 75 months showing 10% more.This means exceeding 10% will be months above 0.9 (from 100-90=90%=1-0.9=0.1 as a decimal)
In the standard normal distribution table, look for 0.9, closest value is 0.8997 which gives z=1.2 for y-axis and for x-axis 0.08 to give 1.28
So you have z=1.28, mean μ=75 and δ=8, finding X will gives
You apply the formula;
P(z>X-75/8)
P(z>1.28)=0.1
z=X-μ /δ
1.28=(X-75)/8
8*1.28=X-75
10.24=X-75
10.24+75=X
X=85.24 months
Learn More
Percentile in Normal distribution :brainly.com/question/13700221
Keywords: normally distributed, mean, standard deviation, exceeds
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