Question

What is the main difference between PERT and CPM?

• A. PERT uses deterministic activity times; CPM uses probabilistic times
• B. CPM uses deterministic activity times; PERT uses probabilistic times
• C. PERT uses deterministic activity times; CPM uses deterministic activity times
• D. CPM uses probabilistic times; PERT uses probabilistic times

Hint:

Remember:
- PERT $\to$ Probabilistic (deals with research where times are unknown)
- CPM $\to$ Construction/Deterministic (deals with established processes)

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
This industrial engineering and project management question asks for the fundamental conceptual distinction between PERT (Program Evaluation and Review Technique) and CPM (Critical Path Method).

Step 2: Key Formula or Approach:
The distinction lies in how the duration of activities is treated in the scheduling models:
- CPM was developed for construction projects with well-known historical data, where activity durations are highly predictable.
- PERT was developed for research and development projects where activity durations are uncertain and must be estimated statistically.

Step 3: Detailed Explanation:

• CPM (Critical Path Method):
- It is a deterministic model.
- Each activity is assumed to have a single, fixed, known duration.
- It is mainly applied to repetitive projects with predictable activities (e.g., construction).

• PERT (Program Evaluation and Review Technique):
- It is a probabilistic model.
- It accounts for uncertainty in activity times by using three time estimates: Optimistic ($t_o$), Most Likely ($t_m$), and Pessimistic ($t_p$).
- The expected duration is calculated using a weighted average: $t_e = \frac{t_o + 4t_m + t_p}{6}$.
- It is mainly applied to non-repetitive, high-uncertainty projects (e.g., R&D, defense projects).

Step 4: Final Answer:
The main difference is that CPM uses deterministic activity times, while PERT uses probabilistic times.