Quick answer
CPM uses single-point durations on the critical path (deterministic); PERT uses three-point estimates (probabilistic) — CPM for known work, PERT for uncertain work.
CPM
Deterministic durations → one critical path, one finish date — for well-understood work.
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PERT
Three-point durations → expected dates + variance — for uncertain, research-type work.
The calculation
CPM: sum the path. PERT: (O+4M+P)/6 per task, then the path — plus variance math.
Choosing
Known construction-style work → CPM; R&D uncertainty → PERT; modern tools blend both.
Bottom line
CPM uses single-point durations on the critical path (deterministic); PERT uses three-point estimates (probabilistic) — CPM for known work, PERT for uncertain work.
FAQ
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