PERT expected time (probabilistic): compute using optimistic, most likely, pessimistic For an activity with three time estimates: tₒ (optimistic), tₙ (most likely), and tₚ (pessimistic). Choose the correct expression for the PERT expected time.
Mechanical Engineering
Industrial Engineering and Production Management
Difficulty: Medium
Choose an option
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A(tₒ + tₙ + tₚ) / 3
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B(tₒ + 4 tₙ + tₚ) / 6
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C(4 tₒ + tₙ + tₚ) / 6
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D(tₒ + 4 tₚ + tₙ) / 6
Answer
Correct Answer: (tₒ + 4 tₙ + tₚ) / 6
Explanation
Approach (Beta distribution assumption)PERT models activity time with a (shifted) beta distribution and uses a weighted mean favouring the most likely time.
Expected time formulate = (tₒ + 4 tₙ + tₚ) / 6
IllustrationIf tₒ = 4, tₙ = 6, tₚ = 10 (days):te = (4 + 4×6 + 10)/6 = (4 + 24 + 10)/6 = 38/6 ≈ 6.33 days.
Common pitfallsDo not average equally; PERT gives 4× weight to the most likely estimate.
Final Answer(tₒ + 4 tₙ + tₚ) / 6.