Operations research
Explainer
PERT: Planning When Durations Are Uncertain
How long will drilling take? PERT asks for three answers, not one.
Quick check · tap an answer to continue
Lesson notes
Key points
- PERT, the Program Evaluation and Review Technique, handles uncertain activity times using three estimates per activity.
- The expected time weights the most likely estimate four times, based on an assumed beta distribution.
- For example, with a equals 4, m equals 6 and b equals 14 days, expected time is 42 divided by 6, which is 7 days.
- Summing expected times and variances along the critical path lets you use the normal distribution to estimate deadline probability.
Definitions
- PERT estimates
- Optimistic a, most likely m, pessimistic b: best, typical and worst-case durations for one activity.
Takeaway: PERT: tₑ = (a + 4m + b) ÷ 6, then sum along the critical path.
Quick check: PERT expected time with a=2, m=5, b=8?
- 5 days
- 4 days
- 6 days
(2 + 20 + 8) ÷ 6 = 30 ÷ 6 = 5 days.
Three estimatesExpected timeWorked exampleProject probability
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