---
title: "Critical path and dummy activity significance"
subject: "Project Engineering"
chapter: 3
key: "semester_7/project_engineering:critical-path-dummy-significance"
source: https://www.bctengineer.com/q/semester_7/project_engineering/critical-path-dummy-significance
site: BCT Engineering
---

# Critical path and dummy activity significance

Project Engineering · Chapter 3: Project Planning and Scheduling

- Asked in: 2082 Baisakh, 2+2 marks
- Video: [Dummy Activity in Network Diagram | Project Management | How to draw a dummy activity? | H K Patel](https://www.youtube.com/watch?v=ChF6FkW4I6c) — Your eStudies
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/project_engineering/critical-path-dummy-significance
- Whole chapter: https://www.bctengineer.com/md/semester_7/project_engineering/chapter-3

## Question

Define and write down the significance of critical path and dummy activities in a network diagram.

## Short answer

The critical path is the longest continuous chain of activities from start to end; it gives the minimum project duration, and its activities have zero float, so delays there delay the whole project. A dummy is a zero-duration, zero-resource dashed arrow that maintains correct logic and unique i-j numbering but consumes no time or resource.

## Answer

#### Critical path

The **critical path** is the longest continuous chain of activities from the start to the end of the project network; it fixes the shortest time in which the project can be completed. Activities on it have zero total float.

**Significance:**
- It gives the minimum project duration.
- Any delay in a critical activity delays the whole project, so these activities need the closest monitoring and the first call on resources.
- To shorten the project, only critical activities should be crashed.
- Non-critical activities have float and can be shifted to level resources.

#### Dummy activity

A **dummy activity** is a zero-duration, zero-resource activity (dashed arrow) used in the arrow diagram.

**Significance:**
- It maintains the correct logical dependence between activities that cannot be shown by arrows alone.
- It gives a unique i-j number to parallel activities.
- It does not consume time or resource, so it does not change the duration, but it may lie on the critical path.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the critical path?
   A. The shortest path in the network
   B. The path with the highest cost
   C. The longest continuous chain from start to end, which fixes the minimum project duration
   D. The path with the most float
   Answer: C. Its length equals the shortest possible project time and its activities have zero total float. (Key point: Critical path definition)

2. What happens if a critical activity is delayed?
   A. The whole project is delayed
   B. Nothing, because float absorbs it
   C. Only the next milestone changes
   D. The project finishes earlier
   Answer: A. Critical activities have no float, so delay passes to the end date. (Key point: Delay effect)

3. Which activities should be crashed to shorten the project?
   A. Only non-critical activities
   B. Only critical activities
   C. All activities equally
   D. Dummy activities
   Answer: B. Shortening non-critical activities does not reduce the longest path. (Key point: Crashing)

4. What is true about a dummy activity?
   A. It increases project duration
   B. It uses one man-day
   C. It can never lie on the critical path
   D. It consumes no time or resource and keeps logic and unique numbering
   Answer: D. A dummy has zero duration but may lie on the critical path. (Key point: Dummy significance)

## Related in Project Engineering

- [Dummy activity; use of critical path in CPM](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Adummy-critical-path-use) — Project Engineering, chapter 3
- [CPM network, 12 activities (A=1 to L=4)](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acpm-network-twelve-act-k81) — Project Engineering, chapter 3, asked 2×
- [Dummy activity and its application](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Adummy-activity-application) — Project Engineering, chapter 3
- [Dummy activity and float definitions](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Afloat-definitions-dummy) — Project Engineering, chapter 3
- [CPM precedence diagram, 9 activities](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acpm-network-precedence-k72) — Project Engineering, chapter 3
- [Critical path, characteristics and importance](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acritical-path-define-characteristics) — Project Engineering, chapter 3

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- [TCTO numerical: crashing critical path, Rs 30/day](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atcto-2069-bhadra) — Construction Management, chapter 2
- [CPM schedule, critical path and float](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_engineering_and_management%3Acpm-network-critical-path-float) — Industrial Engineering and Management, chapter 3