Three-Time Estimates

Activity Network

PERT begins with activity estimates on a small precedence network.

highlighted = computed this step

Activities

The network has 4 activities. Motivation: PERT starts with activity estimates and precedence.

activities=4\text{activities}=4
PERT networkA splits to B and C, then the branches join at D.PERT activity networkexpected project time 7AE=2o,m,p 1,2,3BE=3o,m,p 2,3,4CE=7/3o,m,p 1,2,5DE=2o,m,p 2,2,2A-B-D = 7 criticalA-C-D = 19/3

Split

After A, the project splits into B and C.

A→BA→CA\rightarrow B\quad A\rightarrow C
PERT networkA splits to B and C, then the branches join at D.PERT activity networkexpected project time 7AE=2o,m,p 1,2,3BE=3o,m,p 2,3,4CE=7/3o,m,p 1,2,5DE=2o,m,p 2,2,2A-B-D = 7 criticalA-C-D = 19/3

Join

D waits for both B and C before it can start.

B,C→DB,C\rightarrow D
PERT networkA splits to B and C, then the branches join at D.PERT activity networkexpected project time 7AE=2o,m,p 1,2,3BE=3o,m,p 2,3,4CE=7/3o,m,p 1,2,5DE=2o,m,p 2,2,2A-B-D = 7 criticalA-C-D = 19/3

Expected duration

The expected project time from this model is 7.

expected project time=7\text{expected project time}=7
PERT networkA splits to B and C, then the branches join at D.PERT activity networkexpected project time 7AE=2o,m,p 1,2,3BE=3o,m,p 2,3,4CE=7/3o,m,p 1,2,5DE=2o,m,p 2,2,2A-B-D = 7 criticalA-C-D = 19/3