PERT (Program Evaluation and Review Technique) uses three-time estimates for each activity. Which set correctly represents the PERT basis?
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AOptimistic time only
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BPessimistic time only
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CMost likely time only
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DAll of the above (optimistic, most likely, and pessimistic)
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E—
Answer
Correct Answer: All of the above (optimistic, most likely, and pessimistic)
Explanation
Introduction / Context:PERT is a probabilistic project scheduling technique particularly useful when activity durations are uncertain. It models uncertainty by using three time estimates, allowing computation of an expected duration and variability.
Given Data / Assumptions:
- o = optimistic time (best-case scenario).
- m = most likely time (mode of the distribution).
- p = pessimistic time (worst-case scenario).
Concept / Approach:
PERT assumes a beta distribution for activity times. The expected duration te is calculated using weighted average: te = (o + 4m + p) / 6. The variance is approximated by ((p − o) / 6)^2, capturing spread and risk for project completion time analysis.
Step-by-Step Solution:
Identify that PERT requires all three estimates.Recognize that these are used to compute expected time and variance.Therefore, the correct choice is the set including all three.Verification / Alternative check:
Pertinent references consistently define PERT with the triplet (o, m, p), distinguishing it from CPM's deterministic durations.
Why Other Options Are Wrong:
Any single estimate alone cannot express uncertainty; PERT fundamentally relies on three-point estimation.
Common Pitfalls:
Confusing most likely time with mean; neglecting variance in project risk assessment.
Final Answer:
All of the above (optimistic, most likely, and pessimistic)