Difference between CPM and PERT

Short answer

CPM uses a single deterministic duration and is activity-oriented, allowing time-cost trade-off. PERT uses three time estimates (optimistic, most likely, pessimistic) to compute expected time and is event-oriented, suitable for projects with high uncertainty.

Differentiate between CPM and PERT.

Basis	CPM	PERT
Full form	Critical Path Method	Programme Evaluation and Review Technique
Origin	DuPont, 1957, construction and plant maintenance	US Navy, 1958, Polaris missile project
Time estimate	One deterministic time	Three times: optimistic $a$ , most likely $m$ , pessimistic $b$
Nature	Deterministic	Probabilistic
Expected time	Given duration	$t_e = \dfrac{a + 4m + b}{6}$
Basis	Activity oriented	Event oriented
Cost	Time-cost trade-off (crashing) considered	Mainly time; cost not usually considered
Suitable for	Repetitive, known work (construction)	Research, development and new projects with uncertainty
Output	Critical path and float	Critical path and probability of finishing by a date
Network	Activity-on-arrow or activity-on-node; dummies needed only in activity-on-arrow	Event-based activity-on-arrow network; dummies used where needed

✓ Answer checked by Claude Opus 5.5 (high effort)

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