STEP BY STEP PERT ANALYSIS

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PERT ANALYSIS




Activity
Predecessors
Three time Estimates


a
m
b
A
---
1
2
3
B
A
3
5
7
C
A
6
10
14
D
A
4
6
8
E
B,C,D
8
9
10
F
E
2
4
6
G
F
1
3
5


STEP-1: CALCULATE Te.

Te =  (a+4m+b)/6

Activity
Predecessors
Three time Estimates
Te


a
m
b

A
---
1
2
3
2
B
A
3
5
7
5
C
A
6
10
14
10
D
A
4
6
8
6
E
B,C,D
8
9
10
9
F
E
2
4
6
4
G
F
1
3
5
3


STEP-2: CALCULATE STANDARD DEVIATION (S.D)

S.D = (b-a)/6

Activity
Predecessors
Three time Estimates
Te
S.D


a
m
b


A
---
1
2
3
2
0.33
B
A
3
5
7
5
0.67
C
A
6
10
14
10
1.33
D
A
4
6
8
6
0.67
E
B,C,D
8
9
10
9
0.33
F
E
2
4
6
4
0.67
G
F
1
3
5
3
0.67


STEP 3: CALCULATE VARIANCE(V)

V= (S.D)2

Activity
Predecessors
Three time Estimates
Te
S.D
VARIANCE


a
m
b



A
---
1
2
3
2
0.33
0.11
B
A
3
5
7
5
0.67
0.44
C
A
6
10
14
10
1.33
0.78
D
A
4
6
8
6
0.67
0.44
E
B,C,D
8
9
10
9
0.33
0.11
F
E
2
4
6
4
0.67
0.44
G
F
1
3
5
3
0.67
0.44


STEP 4: CALCULATE VARIANCE FOR THE CRITICAL PATH

(neglect the nodes which are not a part of critical path)

Activity
Predecessors
Three time Estimates
Te
S.D
VARIANCE
VARIANCE OF CRITICAL PATH


a
m
b




A
---
1
2
3
2
0.33
0.11
à 0.11
B
A
3
5
7
5
0.67
0.44
-
(node is not a part of critical path)
C
A
6
10
14
10
1.33
1.78
à1.78
D
A
4
6
8
6
0.67
0.44
-
(node is not a part of critical path)
E
B,C,D
8
9
10
9
0.33
0.11
à0.11
F
E
2
4
6
4
0.67
0.44
à0.44
G
F
1
3
5
3
0.67
0.44
à0.44

STEP-5: CALCULATE TOTAL OF CRITICAL PATH  VARIANCE
Activity
Prede
cessors
Three time Estimates
Te
S.D
VARIANCE
VARIANCE OF CRITICAL PATH


a
m
b




A
---
1
2
3
2
0.33
0.11
à 0.11
B
A
3
5
7
5
0.67
0.44
-
(node is not a part of critical path)
C
A
6
10
14
10
1.33
1.78
à1.78
D
A
4
6
8
6
0.67
0.44
-
(node is not a part of critical path)
E
B,C,D
8
9
10
9
0.33
0.11
à0.11
F
E
2
4
6
4
0.67
0.44
à0.44
G
F
1
3
5
3
0.67
0.44
à0.44
TOTAL OF CRITICAL PATH VARIANCE
2.89


STEP-6: CALCULATE THE S.D OF CRITICAL PATH

S.D = √ (VARIANCE OF CRITICAL PATH)

S.D = √2.89 = 1.699


STEP-7: CALCULATE THE VALUE OF Z

Z = (x - µ) / (S.D)

Z= (39-28)/1.699 = 6.47

Here,
 x= total estimate time ( ∑Te )
µ= ( ∑Te ),  includes only the critical path nodes

STEP 8: CALCULATE THE PROBABILITY

PROBABILITY = NORMSDIST(Z)


PROBABILITY = NORMSDIST(6.47) = 1 = 100%

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HOW TO CALCULATE CRITICAL PATH, FREE FLOAT AND TOTAL FLOAT ?

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Critical Path Method

Activity
Predecessors
Three time Estimates


a
m
b
A
---

2

B
A

5

C
A

10

D
A

6

E
B,C,D

9

F
E

4

G
F

3


here we have not putted the values of a and b as it is not required in calculating the critical path, free float and total float.

Step-1: Draw Network Diagram




Step-2: Find Critical Path


P1: A > B > E > F > G = 23
P2: A > C > E > F > G = 28 -> Highest time = critical path
P3: A > D > E > F > G = 24

Step-3: Calculate Early start, late start, early finish and late finish.

SHOWN IN THE DIAGRAM.

Step-4: Calculate Total float and free float.


TOTAL FLOAT=LATE START - EARLY START



Total Float (TF)                                                                   

A
0-0=0
 B
7-2=5
C
2-2=0
D
6-2=4
E
12-12=0
F
21-21=0
G
25-25=0












FREE FLOAT OF A ACTIVITY= EARLY START OF NEXT ACTIVITY - EARLY FINISH OF CURRENT ACTIVITY

Free float (ff)
A
2-2=0
B
12-7=5
C
12-12=0
D
12-8=4
E
21-21=0
F
25-25=0









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CREATING TABLE, FORMS AND REPORTS IN ACCESS

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