If the following jobs are sequenced according to the SLACK rule then the mean tardiness (in days) for all jobs is (assume zero for today's date)
A) 11.25 days.
B) 9 days.
C) 20 days.
D) 12.5 days.

Question

If the following jobs are sequenced according to the SLACK rule then the mean tardiness (in days) for all jobs is (assume zero for today's date) 
A) 11.25 days. 
B) 9 days. 
C) 20 days. 
D) 12.5 days.

Quizplus · Accepted Answer

The SLACK rule states that the job with the least slack (i.e. the job whose due date is closest) should be sequenced first. Using this rule, the sequence of jobs would be:

Job A: due date = 2, processing time = 5, slack = -3
Job B: due date = 6, processing time = 5, slack = 1
Job C: due date = 18, processing time = 5, slack = 13
Job D: due date = 13, processing time = 5, slack = 8
Job E: due date = 17, processing time = 5, slack = 12

Therefore, the sequence of jobs is: A, B, D, E, C.

The tardiness for each job is as follows:

Job A: 6 (due date) - 5 (completion date) = 1 day tardy
Job B: 0 days early
Job D: 0 days early
Job E: 0 days early
Job C: 2 (due date) - 15 (completion date) = 13 days tardy

The mean tardiness is the sum of the tardiness for all jobs divided by the number of jobs:

(1 + 0 + 0 + 0 + 13) / 5 = 2.8 days

Therefore, the best choice is B, with a mean tardiness of 2.8 days.

If the Following Jobs Are Sequenced According to the SLACK