Question

1. The table shows the jobs to be scheduled and estimated process times for the jobs. The promised delivery times are shown in the table.

Job	process time	delivery due time	slack time
A	4	75
B	16	90
C	2	30
D	27	90
E	5	90
F	38	75
G	26	120

Determine the average process completion time and average delay using (i) the shortest processing time first and (ii) the minimum slack time first dispatch rules.

Answer 1

Here, Important Formulas are

slack time Remaining = Delivery Due time - Process Time

Flow Time = cumulative process time,

Lateness = Flow time - Delivery Due time,

Average process completion time = Total Flow time/ Number of Jobs

Average Delay or lateness = Total Lateness/number of Jobs

For Shortest processing time, we will consider the activities in order of shortest processing time,

For Minimum Slack time, we we will consider the activities in order of Minimum slack time,

1	B	C	D	E	F
2	Job	process time	delivery due time	slack time Remaining = Delivery Due time - Process Time
3	A	4	75	71
4	B	16	90	74
5	C	2	30	28
6	D	27	90	63
7	E	5	90	85
8	F	38	75	37
9	G	26	120	94
10
11	Shortest Processing Time
12	Job	Process time	Flow Time	delivery due time	Lateness
13	C	2	2	30	0
14	A	4	6	75	0
15	E	5	11	90	0
16	B	16	27	90	0
17	G	26	53	120	0
18	D	27	80	90	0
19	F	38	118	75	43
20			Average Process completion Time		Average Lateness
21			42.43		6.14
22
23	Minimum Slack Time
24	Job	Process time	Flow Time	delivery due time	Lateness
25	C	2	2	30	0
26	F	38	40	75	0
27	D	27	67	90	0
28	A	4	71	75	0
29	B	16	87	90	0
30	E	5	92	90	2
31	G	26	118	120	0
32			Average Process completion Time		Average Lateness
33			68.14		0.29

Formula

1	B	C	D	E	F
2	Job	process time	delivery due time	slack time Remaining = Delivery Due time - Process Time
3	A	4	75	=D3-C3
4	B	16	90	=D4-C4
5	C	2	30	=D5-C5
6	D	27	90	=D6-C6
7	E	5	90	=D7-C7
8	F	38	75	=D8-C8
9	G	26	120	=D9-C9
10
11	Shortest Processing Time
12	Job	Process time	Flow Time	delivery due time	Lateness
13	C	2	=C13	30	0
14	A	4	=C14+D13	75	0
15	E	5	=C15+D14	90	0
16	B	16	=C16+D15	90	0
17	G	26	=C17+D16	120	0
18	D	27	=C18+D17	90	0
19	F	38	=C19+D18	75	=D19-E19
20			Average Process completion Time		Average Lateness
21			=AVERAGE(D13:D19)		=AVERAGE(F13:F19)
22
23	Minimum Slack Time
24	Job	Process time	Flow Time	delivery due time	Lateness
25	C	2	=C25	30	0
26	F	38	=C26+D25	75	0
27	D	27	=C27+D26	90	0
28	A	4	=C28+D27	75	0
29	B	16	=C29+D28	90	0
30	E	5	=C30+D29	90	=D30-E30
31	G	26	=C31+D30	120	0
32			Average Process completion Time		Average Lateness
33			=AVERAGE(D25:D31)		=AVERAGE(F25:F31)