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73-220-Lecture18

# 73-220-Lecture18 - ProjectScheduling:PERT/CPM 73-220...

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1 Project Scheduling: PERT/CPM 73-220 Lecture 18

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2 Agenda Review of last class. PERT/CPM with known activity times Project scheduling – PERT/CPM Project scheduling with uncertain activity times Next Class
3 Uncertain Activity Times: Mean In the three-time estimate approach , the time to  complete an activity is assumed to follow a Beta  distribution.   An activity’s mean completion time  is:    a    =  the optimistic  completion time estimate  b    =  the pessimistic  completion time estimate  m   =  the most likely  completion time estimate 4 6 a m b t + + =

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4 Uncertain Activity Times: Variance     An activity’s  An activity’s  completion time variance completion time variance  is:  is:     a a    =  the     =  the  optimistic optimistic  completion time estimate  completion time estimate     b b    =  the     =  the  pessimistic pessimistic  completion time estimate  completion time estimate     m m   =  the    =  the  most likely most likely  completion time estimate  completion time estimate 2 2 6 b a σ - = ÷
5 Overall Completion Time In the three-time estimate approach, the critical  path is determined as if the mean times for the  activities were fixed times.   The overall project completion time  is assumed  to have a  normal distribution  with  mean equal to  the sum of the means along the critical path  and  variance equal to the sum of the variances along  the critical path .

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6 Example: ABC Associates Consider the following project:                        Immed.  Optimistic  Most Likely  Pessimistic      Activity     Predec.    Time (Hr. )   Time (Hr.)    Time (Hr.)           A              --                4              6       8            B               --                1                4.5                   5
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73-220-Lecture18 - ProjectScheduling:PERT/CPM 73-220...

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