The Lockhead Aircraft Co. is ready to begin a project to develop a new fighter airplane for the U.S. Air Force. The company€™s contract with the Department of Defense calls for project completion within 100 weeks, with penalties imposed for late delivery.
The project involves 10 activities (labeled A, B, . . . , J), where their precedence relationships are shown in the following project network.

Using the PERT three-estimate approach, the usual three estimates of the duration of each activity have been obtained as given below.

(a) Find the estimate of the mean and variance of the duration of each activity.
(b) Find the mean critical path.
(c) Find the approximate probability that the project will finish within 100 weeks.
(d) Is the approximate probability obtained in part (c) likely to be higher or lower than the true value?

START FINISH optimlstic MostklyPessimistic Most Likely Estimate Activity Estimate Estimate 28 weeks 22 weeks 26 weeks 14 weeks 32 weeks 40 weeks 12 weeks 16 weeks 26 weeks 12 weeks 32 weeks 28 weeks 36 weeks 16 weeks 32 weeks 52 weeks 16 weeks 20 weeks 34 weeks 16 weeks 36 weeks 32 weeks 46 weeks 18 weeks 32 weeks 74 weeks 24 weeks 26 weeks 42 weeks 30 weeks