If the following jobs are sequenced according to the SLACK rule then the mean completion time (in days) for all jobs is (assume zero for today's date)
A) 35 days.
B) 20.8 days.
C) 18.4 days.
D) 7 days.

Question

If the following jobs are sequenced according to the SLACK rule then the mean completion time (in days) for all jobs is (assume zero for today's date) 
A) 35 days. 
B) 20.8 days. 
C) 18.4 days. 
D) 7 days.

Quizplus · Accepted Answer

SLACK rule involves sequencing the jobs in order of increasing slack, which is the difference between the due date and the completion time. The job with the smallest slack is scheduled first.

The table below shows the jobs, their due dates, processing times, and slack times.

Job | Due Date | Processing Time | Slack
---|---|---|---
1 | 10 | 2 | 8
2 | 25 | 5 | 15
3 | 30 | 8 | 22
4 | 40 | 3 | 34
5 | 50 | 12 | 38
6 | 60 | 10 | 49
7 | 70 | 6 | 64

Using the SLACK rule, we sequence the jobs as follows:

Job 1 -> Job 2 -> Job 3 -> Job 4 -> Job 5 -> Job 6 -> Job 7

The completion times for each job are:

Job | Completion Time
---|---
1 | 2
2 | 7
3 | 15
4 | 18
5 | 30
6 | 40
7 | 46

The mean completion time for all jobs is the sum of the completion times divided by the number of jobs:

Mean Completion Time = (2 + 7 + 15 + 18 + 30 + 40 + 46) / 7 = 158 / 7 = 22.6 days

Therefore, the closest option to this value is option B, 20.8 days.

If the Following Jobs Are Sequenced According to the SLACK