The activities required to service a car at Zippy-Lube can be viewed as a mini-project as summarized in the following table.
Time Required
Activity Description Predecessor Activity Min Most Likely Max
A Drain oil — 2 3.5 5
B Replace filter A 1 2 3
C Refill oil B, E 2 2.5 4
D Check tires — 2 3 4
E Wash windows D 2 3 5
F Fill fluids E 2 3 4
G Final test C, F 0.5 1 1.5
The variability in the time required to perform each activity is due to the different types, sizes, and condition of the cars to be serviced.
a. Draw the activity network for this problem.
b. Use PERT to identify the expected time and variance for each activity.
c. What is the critical path? What is the expected time and variance of the critical path?