Suppose That the Average Time Before Breakdown Is Normally Distributed

Multiple Choice

Suppose that the average time before breakdown is normally distributed with a mean of 2.5 weeks and a standard deviation of .4 weeks. If breakdowns cost an average of $1,200 and preventive maintenance costs $800, what is the optimal maintenance interval?

A) Every .67 weeks
B) Every .33 weeks
C) Every 2.67 weeks
D) Every 3.25 weeks
E) Every 3.12 weeks