The average time before breakdown of a machine is normally distributed and has a mean of nine weeks and a standard deviation of 1.5 weeks. If breakdown cost averages $1,500 and preventive maintenance costs $500, what is the optimal preventive maintenance interval?
A)3.8 weeks
B)8.4 weeks
C)9.6 weeks
D)6.9 weeks
E)7.2 weeks

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The Answer of The average time before breakdown of a machine is normally distributed and has a mean of nine weeks and a standard deviation of 1.5 weeks. If breakdown cost averages $1,500 and preventive maintenance costs $500, what is the optimal preventive maintenance interval?
A)3.8 weeks
B)8.4 weeks
C)9.6 weeks
D)6.9 weeks
E)7.2 weeks

The Average Time Before Breakdown of a Machine Is Normally