PERT

📘 PERT (Program Evaluation and Review Technique)

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🔹 1. Definition

PERT (Program Evaluation and Review Technique) is a project scheduling technique used to estimate the time required to complete a project when activity durations are uncertain.

👉 It focuses on probabilistic time estimation (uncertain environments).

📌 Developed for R&D and complex projects.

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🔹 2. Key Idea of PERT ⭐

PERT assumes that activity time is not fixed but can vary. So it uses three time estimates:

• 🟢 Optimistic time (O) → Best case
• 🟡 Most Likely time (M) → Normal case
• 🔴 Pessimistic time (P) → Worst case

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🔹 3. PERT Formula

🔸 Expected Time (TE)

TE = (O + 4M + P) / 6

👉 This gives a weighted average time estimate.

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🔹 4. Standard Deviation and Variance (Important ⭐)

🔸 Standard Deviation

SD = (P − O) / 6

🔸 Variance

Variance = [(P − O) / 6]²

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🔹 5. Steps in PERT

🔸 Step 1: Identify Activities

• Break project into tasks (WBS)

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🔸 Step 2: Define Dependencies

• Find task sequence

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🔸 Step 3: Draw Network Diagram

• Show activities and relationships

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🔸 Step 4: Assign Time Estimates

• O, M, P for each activity

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🔸 Step 5: Calculate Expected Time

• Use PERT formula

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🔸 Step 6: Find Critical Path

• Longest expected time path

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🔹 6. Example

Activity	O	M	P
A	2	4	6

Calculation:

TE = (2 + 4×4 + 6) / 6
   = (2 + 16 + 6) / 6
   = 24 / 6 = 4 days

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🔹 7. PERT Diagram Description

📌 PERT uses a network diagram (AON/AOA):

• Nodes → Activities
• Arrows → Dependencies
• Each activity shows O, M, P or TE values
• Critical path is highlighted

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🔹 8. Advantages of PERT

• Useful for uncertain and new projects
• Improves time estimation accuracy
• Helps in risk analysis
• Identifies critical activities
• Supports planning of complex projects

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🔹 9. Limitations of PERT

• Time-consuming calculations
• Depends on accurate estimation of O, M, P
• Not suitable for simple projects
• Assumes probability distribution (may not always be accurate)

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🔹 10. PERT vs CPM ⭐ (Very Important)

Feature	PERT	CPM
Time Type	Probabilistic	Deterministic
Focus	Time uncertainty	Cost & time
Estimates	3 (O, M, P)	Single estimate
Use	Research projects	Construction/software
Nature	Flexible	Fixed planning

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🔹 11. Key Terms

• Optimistic time (O) → fastest completion
• Most likely time (M) → normal condition
• Pessimistic time (P) → worst case
• Expected time (TE) → weighted average

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🔹 12. Importance of PERT

• Helps manage uncertain project timelines
• Improves planning accuracy
• Useful for large and complex software projects
• Supports decision-making under risk

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🔹 13. Short Summary

• PERT is a probabilistic scheduling technique
• Uses three time estimates: O, M, P
• Calculates expected time using weighted formula
• Best suited for uncertain and research-based projects

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🔹 14. Quick Exam Answer (2–3 lines)

PERT (Program Evaluation and Review Technique) is a project scheduling technique used to estimate project duration under uncertainty. It uses three time estimates—optimistic, most likely, and pessimistic—to calculate expected time using a weighted average formula.

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🔹 15. Likely Exam Questions

1. Define PERT.
2. What are O, M, and P times in PERT?
3. Write PERT formula for expected time.
4. Differentiate between PERT and CPM.
5. What are the advantages of PERT?
6. Explain standard deviation in PERT.
7. Draw and explain a PERT network diagram.