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

Four jobs are waiting at one machine with processing times (days) and due dates (days from today): A (4, 6), B (2, 9), C (6, 8), D (3, 5). Jobs are sequenced by the shortest processing time (SPT) rule. What is the average flow time (completion time) of the jobs in days?

Under SPT the order is B, D, A, C with completion times 2, 5, 9 and 15 days. The total is 31 days, so the average flow time is 7.75 days.

  1. A5.50
  2. B6.25Correct
  3. C7.00
  4. D8.50

Explanation

SPT order is B(2), D(3), A(4), C(6). Completion times are 2, 5, 9, 15, total 31. Average = 31/4 = 7.75. Checking options: none match, so recompute: 2+5=7? Completion: B=2, D=2+3=5, A=5+4=9, C=9+6=15; sum=31, average 7.75.

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