Question

Sunny Park Tailors has been asked to make three different types of wedding suits for separate customers. The table below highlights the time taken in hours for cutting and sewing? (process1) and delivery? (process2) of each of the suits.

Times Taken for Different Activities? (hours)
Suit	Cut and Sew	Deliver
11	44	22
22	77	77
33	66	55

Assume that orders for suits have been listed in the above table in the order in which they were received.

Using the FCFS rule for? scheduling,the sequence is:

The options are:  

2-3-1

3-2-1

1-2-3

1-3-2

2-1-3

3-1-2

For the schedule developed using the FCFS? rule, the total length of time taken to complete the three suits?(including delivery)? = _____hours ?(enter your response as a whole? number).

Using? Johnson'srule for? 2-machinescheduling, the sequence is:

The options are:  

2-3-1

1-3-2

3-2-1

3-1-2

1-2-3

2-1-3

For the schedule developed using the? Johnson's rule, the total length of time taken to complete the three suits? (including delivery)? = _______hours ?(enter your response as a whole? number).

Of the two developed? schedules,_______rule gets the schedule finished sooner.

The options are: FCFS or Johnsons

Answer 1

Ans a)

Using the FCFS or first come first serve rule, the sequence of operations would be 1-2-3 as in the table, the suits are listed in the order in which they were received.

Ans b)

The total time taken to complete the 3 suits can be seen from the breakdown of processing time.

1) 44 hours to sew and cut suit 1

2) 22 hours to deliver suit 1

3) 77 hours to sew and cut suit 2, which would include the common 22 hours of delivery of suit 1 as the processing of suit 2 can start when suit 1 is out for delivery. Thus the extra time which is exclusive for processing of suit 2 is (77 - 22) hours or 55 hours

4) 77 hours to deliver suit 2

5) 66 hours to sew and cut suit 3, which would include the common 66 hours of delivery of suit 2 as the processing of suit 3 can start when suit 2 is out for delivery. Thus the extra time which is required for delivery of suit 2 is (77-66) hours or 11 hours

6) The last step is the delivery of suit 3, i.e. 55 hours

Thus the total time according to FCFS rule is 44+22+55+66+11+55 = 253 hours

Ans c)

Suit	Process 1	Process 2
11	44	22
22	77	77
33	66	55

According to Johnson's rule,

If the shortest time is for the first machine or process 1, do the job first

If the shortest time is for the second machine or process 2, do the job last

From the above table, we see that the shortest time of 22 hours is for process 2. Hence from johnsons rule, we will do the job (suit1) last

From the remaining table, we see that the shortest time of 55 hours is again for process 2. Hence from johnsons rule, we will do the job (suit3) last

Hence the schedule becomes, 2-3-1

The total time taken to complete the 3 suits can be seen from the breakdown of processing time.

1) 77 hours to sew and cut suit 2

2) 77 hours to deliver suit 2

3) 66 hours to sew and cut suit 3, which would include the common 66 hours of delivery of suit 2 as the processing of suit 3 can start when suit 2 is out for delivery. Thus the extra time for delivery of suit 2 is (77-66) hours or 11 hours

4) 55 hours to deliver suit 3

5) 44 hours to sew and cut suit 1, which would include the common 44 hours of delivery of suit 3 as the processing of suit 1 can start when suit 3 is out for delivery. Thus the extra time which is required for delivery of suit 3 is (55-44) hours or 11 hours

6) The last step is the delivery of suit 1, i.e. 22 hours

Thus the total time according to FCFS rule is 77+66+11+44+11+22 = 231 hours

Thus out of the 2 options, Johnsons rule gets the job done much quicker by 22 hours