Question

Job	Remaining Processing time (days)	Remaining time until due date (days)	Critical ratio (?)
A	20	30
B	30	50
C	10	25
D	16	80
E	18	12

1. Calculate for each job the relative critical ratio.
2. Analyze the calculated critical ratio.
3. Basing on the calculated CR, specify the scheduling order of each job. Justify your answer.
4. Specify and explain a second dispatch rule that can be adopted.   
5. Among the two rules which seems to be the most effective. Justify your answer.

Answer 1

Given:

Job	Remaining Processing time (days)	Remaining time until due date (days)
A	20	30
B	30	50
C	10	25
D	16	80
E	18	12

Calculate for each job the relative critical ratio.

Answer: Critical ratio is calculated as Time remained for due date/ Remiaining processing time.

Therefore, Critical ratio of Job A is 30/20= 1.5

Critical ratios are calculated in the same manner for all the jobs. The calculated critical ratios are included in the table below

Job	Remaining Processing time (days)	Remaining time until due date (days)	Critical ratio
A	20	30	1.5
B	30	50	1.67
C	10	25	2.5
D	16	80	5
E	18	12	0.66

Analyze the calculated critical ratio.

The critical ratio is lowest for Job E. Therefore, it should be scheduled first

Basing on the calculated CR, specify the scheduling order of each job. Justify your answer.

The sequence of job is E-A-B-C-D. The jobs are scheduled based on the their critical ratios. The job with lowest critical ratio is scheduled at the beginnng and subsequent jobs are scheduled in the increasing ratio of critical ratio.

Specify and explain a second dispatch rule that can be adopted.

The second rule which can be adopted is Earliest due date first. Both the methods are expalined below

Job	Remaining Processing time (days)	Remaining time until due date (days)	Critical ratio	Start	Finish	Flow time	Lateness
A	18	12	0.66	0	18	18	6
B	20	30	1.5	18	38	38	8
C	30	50	1.67	38	68	68	18
D	10	25	2.5	68	78	78	53
E	16	80	5	78	94	94	14
mean						59.2	19.8

second dispatch rule: Earliest due date first

Job	Remaining Processing time (days)	Remaining time until due date (days)	Critical ratio	Start	Finish	Flow time	Lateness
E	18	12	0.66	0	18	18	6
A	20	30	1.5	18	28	28	3
B	30	50	1.67	28	48	48	18
C	10	25	2.5	48	78	78	28
D	16	80	5	78	94	94	14
mean						53.2	13.8

Among the two rules which seems to be the most effective. Justify your answer

Among the two methods, the second method: Earliest due date is most effectoive because it has an average lateness less than first method.