In a network planning scenario for remodeling a restaurant, what is the expected completion time for activity G?

• A. 8.5 minutes
• B. 9.5 minutes
• C. 10.0 minutes
• D. 9.0 minutes

Answer: (B)

Estimating an activity’s duration in a network plan when there’s uncertainty is often done with the PERT approach. In PERT you use three time estimates for an activity: optimistic (best-case), most likely (typical), and pessimistic (worst-case). The expected duration is TE = (a + 4m + b) / 6, where a is the optimistic time, m is the most likely, and b is the pessimistic. The activity’s completion time on the project schedule is the earliest start time from its predecessors plus this TE.

Seeing a value of 9.5 minutes as the expected time means the three estimates for activity G were combined through that PERT formula to land on 9.5. For example, with optimistic 8.5, most likely 9.5, and pessimistic 10.5, TE = (8.5 + 4×9.5 + 10.5) / 6 = 57 / 6 = 9.5 minutes. In other words, the 9.5 minutes reflects the weighted average that accounts for uncertainty, rather than a simple average or a single point estimate.