Chapter 14S – Maintenance
33. The average time before breakdown of a machine is normally distributed and has a mean
of 7 weeks and a standard deviation of 1.5 weeks. If breakdown cost averages $2,500 and
preventive maintenance costs $500, what is the optimal preventive maintenance interval?
An optimal maintenance interval is approximately every 5½ weeks.
34. The average time before breakdown of a machine is normally distributed and has a mean
of 9 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?