Question

Six jobs arrived in a sequence as given below:

Jobs	Processing Time (days)
I	4
II	9
III	5
IV	10
V	6
VI	8

Average flow time (in days) for the above jobs using Shortest Processing Time rule is

• A. 139.00
• B. 23.16
• C. 125.00
• D. 20.83

Answer 1

The correct option is D 20.83

According to SPT rule, arranging the processing time in increasing.

Jobs	Processing time (days)
I	4
III	5
V	6
VI	8
II	9
IV	10

Jobs	Flow time (days)
I	0 + 4 = 4
III	4 + 5 = 9
V	4 + 5 + 6 = 15
VI	4 + 5 + 6 + 8 = 23
II	4 + 5 + 6 + 8 + 9 = 32
IV	4 + 5 + 6 + 8 + 9 + 10 = 42
	Total flow time = 125

$\text{Avg. flow time}=\frac{\text{Total flow time}}{\text{Number of jobs}}$

$=\frac{125}{6}=20.83days$