Standard deviations of the four activities of the critical path are 1,2,4,2.
Standard deviation of this critical path = Sum of square root of variance of this corresponding critical path
Standard deviation of critical path
Now we need to find the probability that the project will completed in 38 weeks given that its expected completion time is 40 weeks.
That is, we need to find P(X<38) :
Probability
Thus the probability that the project will be completed in 38 weeks is 0.34.