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Unformatted text preview: ould take into
account the network paths.
Like typical scheduling, the critical path is associated
with the highest calculated sum. Dr. Maged Ezzat Georgy Schedule
Schedule Calculations
The biggest issue we still need to address is how to
deal with the more complex scheme (i.e., probability
probability
distributions) in adding up the numbers.
To overcome this issue, we revert to the socalled
“Central Limit Theory” in statistics.
This theory addresses the summation of probability
distributions.
distributions. Dr. Maged Ezzat Georgy Schedule Calculations
According to the “Central Limit Theorem”:
◦ The summation result is a “Normal Distribution”.
◦ Tsum (expected time for the project) =
sum Σ te (longest path). ◦ Vsum (expected variance for the project) = Σ ve
(longest path). ◦ σsum (expected SD for the project)
Dr. Maged Ezzat Georgy = √ Vsum Back
Back to the
Project Network Again …
te = 8,
σe = 2 te = 5,
σe = 1 te = 10,
σe = 1.5 Tsum = 30
σsum = te = 10,
σe = 2 √13 te = 20,
σe = 3
te = 25,
σe = 4 Dr. Maged Ezzat Georgy Probability of Completion
PERT provides the means to calculate the probability
of
of completion by a certain time/date.
An example …
◦ Probability of completing the project within 52 weeks is
80%.
◦ Probability of completing the project later than 52 weeks
is
is 20%. Dr. Maged Ezzat Georgy Probability
Probability of Completion
Now, how can we calculate this probability???
We use the ztables as follows…
◦ First calculate Z, where Z = (X – Tsum) /
where
◦ Then use the tables: enter with Z...
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This document was uploaded on 01/22/2014.
 Winter '14

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