---
title: "Dummy activity and its application"
subject: "Project Engineering"
chapter: 3
key: "semester_7/project_engineering:dummy-activity-application"
source: https://www.bctengineer.com/q/semester_7/project_engineering/dummy-activity-application
site: BCT Engineering
---

# Dummy activity and its application

Project Engineering · Chapter 3: Project Planning and Scheduling

- Asked in: 2082 Bhadra, 2 marks
- Video: [Dummy Activities](https://www.youtube.com/watch?v=J2YJwGa4rsc) — Juddy Productions
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/project_engineering/dummy-activity-application
- Whole chapter: https://www.bctengineer.com/md/semester_7/project_engineering/chapter-3

## Question

Define dummy activity and explain its application in scheduling.

## Short answer

A dummy activity is an imaginary zero-duration, zero-resource activity shown by a dashed arrow in an arrow network, used only to show logical dependence. It applies when activities share predecessors, gives unique event numbers to parallel activities, and helps the network have one start and one end.

## Answer

A **dummy activity** is an imaginary activity of zero duration and zero resource, shown by a dashed arrow in an arrow (AOA) network. It only shows a logical dependence.

**Applications in scheduling:**
1. **Showing correct logic.** When D depends on A and B but C depends on A only, a dummy from the end of A to the start of D keeps the logic right.
2. **Unique numbering.** When two activities start and end at the same events (parallel activities), a dummy gives them different end events so that each has a unique i-j number.
3. **Connecting events** so that the network has one start and one end event.

```text
Rule: C depends on A only; D depends on A and B

(1) --A--> (2)
(1) --B--> (3)
(2) --C--> (4)
(2) - - dummy - -> (3)
(3) --D--> (5)

Dummy (2)->(3): D starts only after A and B end,
while C starts after A alone.
```

## Check yourself

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

1. What is a dummy activity?
   A. An activity with the longest duration
   B. An imaginary activity of zero duration and resource, drawn as a dashed arrow
   C. A critical activity with zero float
   D. A key event
   Answer: B. A dummy only shows logical dependence. (Key point: Dummy activity)

2. When D depends on A and B but C depends on A only, what is used?
   A. A dummy from B to C
   B. Making C depend on B
   C. A dummy from the end of A to the start of D
   D. Deleting activity B
   Answer: C. The dummy lets D wait for both A and B while C waits for A alone. (Key point: Logic)

3. Why use a dummy for parallel activities?
   A. To give each a unique i-j number by separating end events
   B. To increase their duration
   C. To add resources
   D. To make them critical
   Answer: A. Parallel activities with the same start and end events would otherwise share the same i-j. (Key point: Unique numbering)

## 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
- [Dummy activity and float definitions](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Afloat-definitions-dummy) — Project Engineering, chapter 3
- [Critical path and dummy activity significance](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acritical-path-dummy-significance) — Project Engineering, chapter 3