Explain the difference between CPM and PERT in terms of time estimation.

Explain the difference between CPM and PERT in terms of time estimation.

• A. CPM uses fixed activity durations; PERT uses probabilistic time estimates to account for uncertainty.
• B. CPM uses probabilistic time estimates; PERT uses fixed durations.
• C. CPM does not consider time at all; PERT is time-only.
• D. CPM uses resource leveling; PERT uses no resources.

Answer: (B)

Time estimation in CPM vs PERT hinges on whether activity durations are treated as fixed or uncertain. In CPM, each activity duration is considered a fixed, known value, so the project timeline is deterministic and there’s a single critical path that sets the finish date. PERT treats time as probabilistic: for each activity you use three estimates—optimistic, most likely, and pessimistic—and from those you derive an expected duration and usually a variance. This turns the overall project completion time into a distribution, allowing you to assess the likelihood of meeting deadlines and to manage risk. So the correct distinction is that CPM uses fixed durations, while PERT uses probabilistic time estimates. The other statements misrepresent how time is handled or add claims about resources that aren’t the core difference.

Time estimation in CPM vs PERT hinges on whether activity durations are treated as fixed or uncertain. In CPM, each activity duration is considered a fixed, known value, so the project timeline is deterministic and there’s a single critical path that sets the finish date. PERT treats time as probabilistic: for each activity you use three estimates—optimistic, most likely, and pessimistic—and from those you derive an expected duration and usually a variance. This turns the overall project completion time into a distribution, allowing you to assess the likelihood of meeting deadlines and to manage risk.

So the correct distinction is that CPM uses fixed durations, while PERT uses probabilistic time estimates. The other statements misrepresent how time is handled or add claims about resources that aren’t the core difference.