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 24 3 B400 26 4 C850 41 6 Preventive Breakdown Equipment Maintenance Cost Cost A201 $290 $2,190 B400 $190 $3,490 C850 $540 $4,725 Click here for the Excel Data File Equipment A201 B400 C850 Probability Ratio Z Interval (days)