Project Networks: Critical Path Method (CPM)

📘 Project Networks: Critical Path Method (CPM)

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🔹 1. Definition

The Critical Path Method (CPM) is a project scheduling technique used to find the longest sequence of dependent activities in a project, which determines the minimum project completion time.

👉 It is used in Project Network Diagrams to plan, schedule, and control activities.

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🔹 2. What is a Project Network?

A project network is a graphical representation of:

• Activities
• Dependencies
• Sequence of tasks

👉 It shows which task comes before or after another task.

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🔹 3. Key Concept of CPM ⭐

The Critical Path is the path with the maximum total duration in the project network.

👉 Important rule:

• Any delay in a critical activity → delays the entire project

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🔹 4. Types of Activities in CPM

🔸 1. Critical Activities

• Must be completed on time
• Have zero slack (float)

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🔸 2. Non-Critical Activities

• Have flexibility (slack time)
• Delay does not affect total project duration

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🔹 5. Steps in CPM

🔸 Step 1: Identify Activities

• Break project into tasks (WBS)

🔸 Step 2: Define Dependencies

• Determine order of tasks

🔸 Step 3: Draw Network Diagram

• Represent activities as nodes/arrows

🔸 Step 4: Estimate Time

• Assign duration to each activity

🔸 Step 5: Find All Paths

• List all possible paths from start to end

🔸 Step 6: Calculate Path Duration

• Add durations of each path

🔸 Step 7: Identify Critical Path

• Longest path = Critical Path

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🔹 6. Formula (Basic Idea)

No complex formula, but:

Critical Path = Path with Maximum Total Duration

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🔹 7. Example

Activities:

Activity	Duration
A → B → D	5 + 3 + 4 = 12 days
A → C → D	5 + 2 + 4 = 11 days

👉 Critical Path = A → B → D (12 days)

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🔹 8. Diagram Description

📌 CPM is shown using a Network Diagram (AON or AOA):

• Nodes → Activities
• Arrows → Dependencies
• Numbers → Time duration

👉 The longest path is highlighted as critical path

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🔹 9. Key Terms

🔸 Float / Slack

• Extra time an activity can be delayed without affecting project

🔸 Earliest Start (ES)

• Earliest time an activity can begin

🔸 Latest Finish (LF)

• Latest time without delaying project

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🔹 10. Advantages of CPM

• Helps in project planning and scheduling
• Identifies critical tasks
• Improves time management
• Useful for cost and resource control
• Helps avoid project delays

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🔹 11. Limitations of CPM

• Time estimates are fixed (deterministic)
• Not suitable for high uncertainty projects
• Complex for large projects
• Requires accurate data

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🔹 12. CPM vs PERT (Important Comparison)

Feature	CPM	PERT
Time	Deterministic	Probabilistic
Focus	Cost & time control	Time uncertainty
Use	Construction, software	Research projects
Estimates	Single time estimate	Three-point estimate

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🔹 13. Important Exam Points

• CPM = Critical Path Method
• Finds longest path in project network
• Critical path determines project duration
• No slack in critical activities
• Delay in critical path → project delay

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🔹 14. Short Summary

• CPM is a network-based scheduling technique
• It identifies the critical path (longest duration path)
• Helps manage time, cost, and resources effectively
• Used widely in software and construction projects

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🔹 15. Quick Exam Answer (2–3 lines)

The Critical Path Method (CPM) is a project scheduling technique used to determine the longest sequence of dependent activities in a project network. This path, called the critical path, defines the minimum time required to complete the project.

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🔹 16. Likely Exam Questions

1. Define Critical Path Method (CPM).
2. What is a critical path?
3. Explain steps of CPM.
4. Differentiate between critical and non-critical activities.
5. Draw and explain a project network diagram.
6. What is slack in CPM?
7. Compare CPM and PERT.