ES Earliest Starting (time)
EF Earliest Finishing
LS Latest Starting
LF Latest Finishing
Slack Extra Time
a optimistic time
m most likely time
b pessimistic time
t = E(T) expected time = (a + 4m + b)/6
V(T) variance = (b - a)2/36
What if activity times are variable?
Activity TimeExpected Value and Variance
a m b t V(T)
A 4 5 6 5 4/36
B 4 5 12 6 64/36
C 1 4 7 4 36/36
D 1 2 3 2 4/36
• What is the probability that the project takes at
least 10 days?
• What is the probability that the project takes less
than 7 days?