PERT Expected Time and Variance

t_{e} = \frac{t _{o} + 4 t _{m} + t _{p}}{6}, σ = \frac{t _{p} - t _{o}}{6}

Beta approximation: mean te and σ from optimistic/most-likely/pessimistic. Path variance is Σσ² along a path (independence). P(finish) from z=(T−Σte)/√Σσ².

$t o, t m, tp$: Optimistic, most likely, pessimistic
$t e$: Expected duration

Step-by-step solved example

to=4, tm=6, tp=14 days. te and σ?

Three times on an activity: to, tm, tp → te, σ.

1. te
(4+24+14)/6=7.0 d.
2. σ
(14−4)/6=1.67 d.

Answer: te=7 d, σ=1.67 d

10 practice questions

0/10 correct

1.If to=tm=tp=5, te=

2.Variance of an activity is

3.Critical path in PERT uses

4.Two sequential σ=2 and 3: σ_path=

5.z= (T−μ)/σ with μ=Σte

6.to=2, tm=3, tp=4: te=

7.PERT is more useful than CPM when

8.A large (tp−to) means

9.Finish probability 84% is about

10.Merge bias means