7 At Tucson Mills, minor breakdowns of machines occur frequently. The occurrence of break- downs and the service time to fix the machines are randomly distributed. Management is con- cemed with minimizing the cost of breakdowns. The cost per hour for the machines to be down is $40. The cost of service repairpersons is $12 per hour. A preliminary study has produced the following data on times between successive breakdowns and their service times:

Simulate 30 breakdowns under two conditions: with one service repairperson and with two service repairpersons. Use the following random number sequence to determine time between breakdowns: RN: 85, 16, 65, 76, 93, 99, 65, 70, 58, 44, 02, 85, 01, 97, 63, 52, 53, 11, 62, 28, 84, 82, 27, 20, 39, 70, 26, 21, 41, 81 Use the following random number sequence to determine service times: RN: 68, 26, 85, 11, 16, 26, 95, 67, 97, 73, 75, 64, 26, 45, 01, 87, 20, 01, 19, 36, 69, 89, 81, 81, 02, 05, 10, 51, 24, 36

a. Using the results of the simulations, calculate (1) The total idle time for the service repairpersons under each condition. (2) The total delay caused by waiting for a service repairperson to begin working on a breakdown.

b. Determine the lowest-cost approach.

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RELATIVE FREQUENCY OF BREAKDOWNS Time between breakdowns (in minutes) Relative frequency 4 5 6 7 8 .10 .30 .25 .20 09 9 .10 .05 RELATIVE FREQUENCY OF SERVICE TIMES Service time (in minutes) Relative frequency 4 5 6 7 8 9 .10 .40 .20 .15 .10 .05