PERT (Program Evaluation and Review Technique) uses three-time estimates for each activity. Which set correctly represents the PERT basis?

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:

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)