1.
I assume you have drawn your own network diagram.
Activity
Precedes
Duration
A
-
9
B
A,D
6
C
B
5
D
-
6
E
D
8
F
E
4
G
C,F
12
Crash this project to 27 weeks using the lowest amount of money
Activity
A
B
C
D
E
F
G
Normal
Duration
9
6
5
6
8
4
12
Crashed
Duration
7
5
4
4
6
3
11
Paths:
ABCG = 32 ----- (Critical Path)
DBCG = 29
DEFG = 30
Crash Cost
720
290
360
320
510
320
650
Normal
Cost
560
240
330
240
370
270
590
2600
Cost Slope
80
50
30
40
70
50
60
Time
Constraint
2
1
1
2
2
1
1
Step 1: Start from the critical path activities and choose the activity with the lowest cost slope to
crash. Remember to consider the allowance. Eg you can only crash C, the lowest slope by 1
week.
Crash C by 1 week
ABCG = 31 ---- (CP)
DBCG = 28
DEFG = 30
Cost = 30 x 1 = 30
Step 2: Focus on the critical path activities and choose the activity with the lowest cost slope to
crash
Crash B by 1 week
ABCG = 30 ---- (CP)
DBCG = 27
DEFG = 30------ (CP)
Cost = 50
Step 3:
Crash D by 2
ABCG = 30 --- (CP)
DBCG = 25
DEFG = 28
Cost – 40x2 = 80
Step 4:
Crash G by 1 week
ABCG = 29 ---- (CP)
DBCG = 24
DEFG = 27
Cost = 60
Step 5
Crash A by 2
ABCG = 27 (CP)
DBCG = 24
DEFG = 27 (CP)
Cost = 80x2 = 160
Remember the potential question of the risk of this set up and how to answer it.
Total crash cost = 30 + 50 + 80 + 60 + 160 = 380
Total project cost = 2600+380 = 2980
2. Assume you have drawn your network diagram
Activity
Precedes
Nd
Cd
Nc
A
-
9
6
10
B
-
8
5
9
C
A
5
4
7
D
A
8
6
9
E
B
7
3
7
F
C
5
5
5
G
D,E
5
2
8
Activity Dependency Tn
(Normal
Time) Weeks
Tc
(Crashed
Time) –
Weeks
A
9
6
Cc
(Crashed
Cost in
Thousand
ZAR)
16
Cn
Cost
(Normal Slope
Cost in
Thousand
ZAR)
10
2
Time
Constraint
B
8
5
18
9
3
3
3
C
A
5
4
8
7
1
1
D
A
8
6
19
9
5
2
E
B
7
3
15
7
2
4
F
C
5
5
5
5
-
0
G
D,E
5
2
23
8
Your CEO has instructed that the project be completed in 15 weeks.
What is the least costly way to reduce the project to 15 weeks?
And how much is the new budget of the project?
(Show all your steps and assumptions).
ADG – 22; ACF – 19; BEG – 20
Step 1: Reduce A by 2
ADG = 20
ACF = 17
BEG = 20
Amount spent in Step 1 = 2*2 = 4
We now have 2 critical paths
Step 2: Reduce A and E by 1 each
ADG = 19
ACF = 16
BEG = 19
Amount spent in Step 2 = 2*1 + 2*1 = 4
Step 3: Reduce G by 3 weeks
ADG = 16
ACF = 16
BEG = 16
Amount spent in Step 3 = 3*5 = 15
Step 4: Reduce E,D and C by 1 each
ADG = 15
ACF = 15
BEG = 15
Amount spent in Step 4 = 2*1 + 5*1 + 1*1 = 8
Amount in total spent to get to 15 weeks= 4+4+15+8 = 31K ZAR
The normal cost of the project is 55K.
Total spent on project:
55K + 31K
= 86K ZAR
5
3