If the following jobs are sequenced according to the SPT rule,then the mean completion time (in days)for all jobs is (assume zero for today's date)
A)6.6 days.
B)16 days.
C)22 days.
D)33 days.

Question

If the following jobs are sequenced according to the SPT rule,then the mean completion time (in days)for all jobs is (assume zero for today's date) 
A)6.6 days. 
B)16 days. 
C)22 days. 
D)33 days.

Quizplus · Accepted Answer

SPT (shortest processing time) rule sequences jobs in order of their processing times, so that the shortest job is scheduled first.

Using SPT rule, we have the following sequence:

Job 1: Process time = 2 days 
Job 2: Process time = 3 days 
Job 5: Process time = 5 days 
Job 3: Process time = 7 days 
Job 4: Process time = 8 days

The completion time for each job is as follows:

Job 1: 2 days (completed on day 2) 
Job 2: 5 days (completed on day 5) 
Job 5: 10 days (completed on day 10) 
Job 3: 17 days (completed on day 17) 
Job 4: 25 days (completed on day 25)

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

Mean completion time = (2 + 5 + 10 + 17 + 25)/5 = 11.8 days

Therefore, the best choice is B) 16 days, as it is the closest option to the calculated mean completion time.

If the Following Jobs Are Sequenced According to the SPT