The following table contains information regarding jobs that are to be scheduled

Question

The following table contains information regarding jobs that are to be scheduled through one machine. Assume jobs are listed in order of arrival (i.e., A, then B, then C, etc.).

Round your answers to 1 decimal place.

a. What is the first-come, first-served (FCFS) schedule?

b. What is the shortest operating time (SOT) schedule?

c. What is the slack time remaining (STR) schedule?

d. What is the earliest due date (EDD) schedule?

e. What are the mean flow times for each of the schedules above?

rev: 08_11_2017_QC_CS-95267

JOB PROCESSING
TIME (DAYS) DUE
DATE     A 7 22     B 15 29     C 3 19     D 9 17     E 10 14     F 2 4     G 5 10

Explanation / Answer

Flow time = cumulative Sum of the processing time. This formula will be used to calculate the flow time for each job in all the sequencing rules.

a) According to the First come first served rule jobs are Scheduled on the basis of their arrival. The job that arrives first is scheduled first. So according to this rule the sequence is

Job processing time flow time

A 7 7

B 15 22

C 3 25

D 9 34

E 10 44

F 2 46

G 5 51

b) According to the shortest operating time rule the jobs are sequenced according to their operating or processing time in an ascending order. This means the job with the shortest processing time is scheduled first. So according to this rule the sequence is

Job processing time flow time

F 2 2

C 3 5

G 5 10

A 7 17

D 9 26

E 10 36

B 15 51

c) slack time remaining = due date - processing time.

Using the above formula the slack time remaining for each job are:

c) According to the slack time remaining rule the jobs are sequenced according to the slack time remaining in ascending order. This means the job with the shortest slack time remaining is scheduled first So according to this rule the sequence is.

Job processing time flow time

F 2 2

E 10 12

G 5 17

D 9 26

B 15 41

A 7 48

C 3 51

d) According to the Earliest due date rule the jobs are sequenced according to the earliest due date. This means the job with the earliest due date is scheduled first. So according to this rule the sequence is

Job processing time flow time

F 2 2

G 5 7

E 10 17

D 9 26

C 3 29

A 7 36

B 15 51

e) Mean flow time = Sum of the flow time for each jobs / number of jobs

Using the above formula the mean flow time for each sequencing rule are

For FCFS = (7+22+25+34+44+46+51)/7 = 229/7 = 32.7

For SOT =(2+5+10+17+26+36+51)/7 = 147/7 = 21

For STR = (2+12+17+26+41+48+51)/7 = 197/7 = 28.1

For EDD =(2+7+17+26+29+36+51)/7 = 168/7 = 24

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