---
title: "Critical activities and float definition"
subject: "Project Engineering"
chapter: 3
key: "semester_7/project_engineering:float-definitions-critical-activities"
source: https://www.bctengineer.com/q/semester_7/project_engineering/float-definitions-critical-activities
site: BCT Engineering
---

# Critical activities and float definition

Project Engineering · Chapter 3: Project Planning and Scheduling

- Asked in: 2072 Chaitra, 2 marks
- Video: [Project Management: Finding the Critical Path(s) and Project Duration](https://www.youtube.com/watch?v=uCR2x-VyxLg) — Excel@Analytics - Dr. Canbolat
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/project_engineering/float-definitions-critical-activities
- Whole chapter: https://www.bctengineer.com/md/semester_7/project_engineering/chapter-3

## Question

Define critical activities and float.

## Short answer

Critical activities lie on the longest path and have zero total float; any delay in them delays the entire project. Float (slack) is spare time available for an activity, allowing it to be delayed or extended without affecting the project completion date. Main types are total float (LFT – EFT), free float, interfering float, and independent float.

## Answer

**Critical activities** are the activities of a network that lie on the critical (longest) path; they have zero total float (EST = LST and EFT = LFT), so any delay in them delays the whole project.

**Float** (slack) is the spare time available to an activity: the time by which it can be delayed or extended without delaying the project completion. The main types are total float $(LFT - EFT)$, free float, interfering float and independent float.

## Check yourself

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

1. What is a critical activity?
   A. One with the longest duration
   B. One on the longest path with zero total float
   C. One with the largest float
   D. One with zero duration
   Answer: B. Critical activities have EST = LST and EFT = LFT. (Key point: Critical activity)

2. What is float?
   A. Spare time by which an activity can be delayed or extended without delaying project completion
   B. The duration of an activity
   C. The cost of an activity
   D. The resources of an activity
   Answer: A. Float is the slack available to an activity. (Key point: Float)

3. Which is a type of float?
   A. Early, late and mean
   B. Optimistic and pessimistic
   C. Total, free, interfering and independent
   D. Planned and actual
   Answer: C. These are the standard float types. (Key point: Types)

## Related in Project Engineering

- [CPM network, 10 activities (A=4 to J=9)](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acpm-network-ten-act-as70) — Project Engineering, chapter 3
- [CPM network, 10 activities with successors](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acpm-network-ten-act-a74) — 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×
- [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 and dummy activity significance](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acritical-path-dummy-significance) — 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

## Related in other subjects

- [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
- [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