CPM vs. PERT – time estimates In Critical Path Method (CPM), activity durations are typically treated using which type of time estimate?

Introduction / Context:
Project network methods include CPM and PERT. Though both identify a critical path, their treatment of activity time is different, affecting how uncertainty is modeled.

Given Data / Assumptions:

• CPM is commonly used where durations can be estimated reliably or controlled (e.g., construction, maintenance turnarounds).
• PERT is used where activity times are uncertain and variable (e.g., R&D).

Concept / Approach:
CPM assumes a single, deterministic duration for each activity and emphasizes time–cost trade-offs (crashing). PERT uses three-point estimates to compute expected time and variance.

Step-by-Step Solution:
Assign a single duration to each activity in CPM.Perform forward and backward passes to find ES, EF, LS, LF, and total float.Identify zero-float activities forming the critical path and the project duration.Optionally, analyze crashing by shortening durations at extra cost to meet a target deadline.

Verification / Alternative check:
Comparing CPM with PERT on the same project shows CPM's deterministic schedule versus PERT's probability-based completion dates.

Why Other Options Are Wrong:
Options (b), (c), and (e) reflect PERT-style probabilistic modeling. Option (d) is incorrect—time estimates are central to both CPM and PERT.

Common Pitfalls:
Using CPM without considering variability where it is significant; ignoring resource constraints may make the schedule unrealistic.

Final Answer:
Single time estimate (deterministic duration)