---
title: "CPM and PERT and their uses"
subject: "Project Engineering"
chapter: 3
key: "semester_7/project_engineering:cpm-pert-uses"
source: https://www.bctengineer.com/q/semester_7/project_engineering/cpm-pert-uses
site: BCT Engineering
---

# CPM and PERT and their uses

Project Engineering · Chapter 3: Project Planning and Scheduling

- Asked in: 2065 Shrawan (old course), 5 marks
- Video: [Network Charts: What's the Difference between PERT and CPM?](https://www.youtube.com/watch?v=zpT0tBGW4-E) — Online PM Courses - Mike Clayton
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/project_engineering/cpm-pert-uses
- Whole chapter: https://www.bctengineer.com/md/semester_7/project_engineering/chapter-3

## Question

Explain CPM and PERT and their uses.

## Short answer

CPM uses deterministic time estimates to find the critical path, project duration and floats, and supports time-cost trade-off, suitable for construction projects with known durations. PERT uses three probabilistic time estimates (optimistic, most likely, pessimistic) to find expected duration and probability of completion, suitable for research and development projects with uncertain times.

## Answer

#### CPM (Critical Path Method)

CPM was developed in 1957 by Du Pont and Remington Rand for plant maintenance and construction. It is a network technique with **deterministic** (single) time estimates for each activity. It finds the critical path, project duration and floats, and links time with cost (cost-time trade-off).

#### PERT (Programme Evaluation and Review Technique)

PERT was developed in 1958 by the US Navy for the Polaris missile project. It is **probabilistic**: three time estimates are used - optimistic $t_o$, most likely $t_m$ and pessimistic $t_p$.

$$
t_e = \frac{t_o + 4t_m + t_p}{6}, \qquad \sigma = \frac{t_p - t_o}{6}
$$

It is event oriented and gives the probability of finishing by a given date.

#### Uses

| CPM | PERT |
|---|---|
| Construction projects (roads, buildings, bridges) with known durations | Research, development and new, first-time projects |
| Finding critical path and floats | Estimating the chance of meeting a deadline |
| Time-cost trade-off and crashing | Projects where time estimates are uncertain |
| Resource levelling and scheduling | Planning and review of big programmes such as defence and hydropower tunnelling |
| Monitoring and updating the schedule | Control of time (cost is not the main concern) |

Both help to plan, schedule and control large projects, show inter-dependence of activities, and focus management attention on critical activities.

## Check yourself

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

1. What kind of time estimate does CPM use?
   A. Deterministic, a single estimate
   B. Three probabilistic estimates
   C. No estimate
   D. Only pessimistic
   Answer: A. CPM uses one duration per activity. (Key point: CPM time estimate)

2. What is the PERT expected time?
   A. (to + tm + tp)/3
   B. (to + 4tm + tp)/6
   C. (to + 4tp + tm)/6
   D. (tp - to)/6
   Answer: B. The weighted average gives te; (tp - to)/6 is the standard deviation. (Key point: PERT formula)

3. Which use belongs to CPM?
   A. Estimating chance of meeting a deadline
   B. Research projects with no data
   C. Event-oriented probability analysis
   D. Time-cost trade-off and crashing
   Answer: D. CPM links time with cost; PERT suits uncertain new projects. (Key point: Use)

## Related in Project Engineering

- [Difference between CPM and PERT](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acpm-vs-pert-difference) — Project Engineering, chapter 3, asked 2×
- [When to use bar chart, CPM, PERT](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Abar-chart-cpm-pert-situations) — Project Engineering, chapter 3
- [CPM vs PERT; te and variance for x, y](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Acpm-pert-te-variance-x-y) — Project Engineering, chapter 3
- [PERT mean and SD of two projects](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Apert-mean-sd-two-projects) — Project Engineering, chapter 3

## Related in other subjects

- [Bar chart vs CPM/PERT as planning tool](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Aplanning-tool-choice) — Construction Management, chapter 2, asked 3×
- [Difference between CPM and PERT](https://www.bctengineer.com/question.md?key=semester_7%2Fict_project_management%3Acpm-vs-pert) — ICT Project Management, chapter 8
- [Difference between CPM and PERT](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_engineering_and_management%3Adifference-between-cpm-and-pert) — Industrial Engineering and Management, chapter 3