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CMA Intermediate · Operations Management and Strategic Management · Scheduling and Queuing Models

Four jobs with processing times A = 5, B = 2, C = 4, D = 3 days are loaded on one machine from time zero. Their due dates are A = 14, B = 4, C = 9, D = 6. If they are sequenced by earliest due date (EDD), what is the average flow time (mean completion time) of the jobs?

Sequencing by earliest due date gives the order B, D, C, A. Their completion times are 2, 5, 9 and 14 days, totalling 30. Dividing by four jobs gives an average flow time of 7.5 days.

  1. A6.0 days
  2. B7.5 daysCorrect
  3. C8.0 days
  4. D9.5 days

Explanation

EDD order by due date: B (4), D (6), C (9), A (14). Completion times: B = 2, D = 2+3 = 5, C = 5+4 = 9, A = 9+5 = 14. Sum = 2+5+9+14 = 30; average = 30/4 = 7.5 days. Check: no job is late as 2<=4, 5<=6, 9<=9, 14<=14.

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