The lifetime of a particular component is normally distributed with a mean of 1000 hours and a standard deviation of 100 hours. What is the 80th percentile of component lifetimes? Question 13 options: 84 1254 1157 1084
X : lifetime of a particular component
X is normally distributed with a mean of 1000 hours and a standard deviation of 100 hours
Let X80 be the 80th percentile of component lifetimes
Therefore,
P(X X80) = 0.80
Z80 be the Z-score of X80
Z80 = (X80 -mean)/Standard deviation = (X80 - 1000)/100
X80 = 1000+100Z80
P(ZZ80) = P(X X80) = 0.80
From standard normal tables,
P(Z0.84) =0.79950.80
Z80 = 0.84
X80 = 1000+100Z80 =1000+100 x 0.84 = 1000+84 = 1084
X80 = 1084
80th percentile of component lifetimes = 1084
Answer : 1084
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