Page 151 - DCAP601_SIMULATION_AND_MODELING

Unit 9: Simulation of a PERT Network (I)

9.2.4 Drawing the CPM/PERT Network Notes

Each activity (or sub-project) in a PERT/CPM Network is represented by an arrow symbol. Each
activity is preceded and succeeded by an event, represented as a circle and numbered.

At Event 3, we have to evaluate two predecessor activities - Activity 1-3 and Activity 2-3, both of
which are predecessor activities. Activity 1-3 gives us an Earliest Start of 3 weeks at Event 3.
However, Activity 2-3 also has to be completed before Event 3 can begin. Along this route, the
Earliest Start would be 4+0=4. The rule is to take the longer (bigger) of the two Earliest Starts. So
the Earliest Start at event 3 is 4.

Similarly, at Event 4, we find we have to evaluate two predecessor activities - Activity 2-4 and
Activity 3-4. Along Activity 2-4, the Earliest Start at Event 4 would be 10 wks, but along Activity
3-4, the Earliest Start at Event 4 would be 11 wks. Since 11 wks is larger than 10 wks, we select it
as the Earliest Start at Event 4.

Notes We have now found the longest path through the network. It will take 11 weeks
along activities 1-2, 2-3 and 3-4. This is the Critical Path.

The Backward Pass - Latest Finish Time Rule

To make the Backward Pass, we begin at the sink or the final event and work backwards to the
first event.

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