Question

Vicki’s Office Cleaners are responsible for the annual major cleaning of university buildings. The job requires mopping (1st activity) and waxing (2nd activity) of each building. Vicki wants to minimize the time it takes her crews to finish cleaning (minimize make-span) the five buildings. She needs to finish in 20 days

time required for each building on each activity
	activity1	activity 2
buildings	mopping days	waxing days
Hall A	1	2
Hall B	3	5
Hall C	2	4
Hall D	5	4
Hall E	4	2

Using Johnson’s rule for scheduling, what will be the job sequence?

time required for each building
	activity 1	activity 2
buildings	mopping	waxing
?	?	?
?	?	?
?	?	?
?	?	/
?	?	?

activity days

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

mopping

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

waxing

?

?

?

?

?

?

?

?

?

?

?

?

/

?

?

?

?

?

Answer 1

Minimum make-span schedule is obtained using Johnson's rule as follows:

------------------------

Resulting activity chart is following:

Activity days

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Mopping

A

C

C

B

B

B

D

D

D

D

D

E

E

E

E

Waxing

A

A

C

C

C

C

B

B

B

B

B

D

D

D

D

E

E

Actual time taken to complete all the tasks = 18 days