(5 points) Wear related failures of an Exhaust Valve Seat follows a lognormal di
ID: 3358824 • Letter: #
Question
(5 points) Wear related failures of an Exhaust Valve Seat follows a lognormal distribution with a log-mean of 7 and log standard deviation of 1.5. 10% of the items will failure before what time-in-service, in thousands of miles? 015 U.9975 0.9976 0.9977 0.9977 0.9978 0.9979 0.9979 I 0.9982 0.9982 0.9983 0.9984 0.9984 0.9985 0.9985 0.9986 0.9986 9 0.9987 0.9987 0.9988 0.9988 0.9989 0.9989 0.9989 0.9990 0.9990 0.9991 0.9991 0.9991 0.9992 0.9992 0.9992 0.9992 0.9993 0.9993 0.9993 0.9994 0.9994 0.9994 0.9994 0.9994 0.9995 0.9995 0.9995 0.9995 0.9995 0.9996 0.9996 0.9996 0.9996 0.9996 0.9996 0.9997 0.9997 0.9997 0.9997 0.9997 0.9997 0.9997 0.9997 0.9997 0.9998Explanation / Answer
Log-mean = 7
Log-stdev = 1.5
Z = Ln(x)-7 / 1.5
Z for .10 is -1.28
So, -1.28 = Ln(x)-7 / 1.5
Ln(X) = -1.28*1.5+7= 5.08
X = e^5.08 = 160.774
10% of items will fail before 160.774 hours
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