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.

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 formula
t_e = (tₒ + 4 tₙ + tₚ) / 6

Illustration
If tₒ = 4, tₙ = 6, tₚ = 10 (days):t_e = (4 + 4×6 + 10)/6 = (4 + 24 + 10)/6 = 38/6 ≈ 6.33 days.

Common pitfalls
Do not average equally; PERT gives 4× weight to the most likely estimate.

Final Answer
(tₒ + 4 tₙ + tₚ) / 6.