Determine the optimum preventive maintenance frequency for each of the pieces of equipment if breakdown time is normally distributed: (Round "Probability Ratio" to 4 decimal places, and all other answers to 2 decimal places. Negative values should be indicated by a minus sign.) Use Table. Average Time (days) Standard Equipment between Breakdowns Deviation A201 20 2 B400 30 3 C850 40 4 Preventive Breakdown Equipment Maintenance Cost Cost A201 $300 $2,300 B400 $200 $3,500 C850 $530 $4,800 Click here for the Excel Data File Equipment A201 B400 C850 Probability Ratio Z Interval (days)