---
title: "PageRank"
subject: "Information System"
chapter: 7
key: "semester_8/information_system:pagerank"
source: https://www.bctengineer.com/q/semester_8/information_system/pagerank
site: BCT Engineering
---

# PageRank

Information System · Chapter 7: Web based information system and navigation

- Asked in: 2070 Bhadra, 3 marks
- Video: [How Google's PageRank Algorithm Works](https://www.youtube.com/watch?v=meonLcN7LD4) — Spanning Tree
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/information_system/pagerank
- Whole chapter: https://www.bctengineer.com/md/semester_8/information_system/chapter-7

## Question

What is PageRank?

## Short answer

PageRank is a link analysis algorithm that assigns importance scores to web pages based on the number and quality of incoming links. It uses iterative computation: PR(A) = (1-d) + d * Σ(PR(Ti)/C(Ti)), with damping factor d typically 0.85. A page's score is like the probability a random surfer visits it.

## Answer

**PageRank** is a link analysis algorithm, developed by Larry Page and Sergey Brin (Google), that gives each web page a numerical score of its importance based on the number and quality of pages linking to it. A link from page A to B is counted as a vote for B, and a vote from an important page counts more.

#### Formula
PR(A) = (1 - d) + d × ( PR(T1)/C(T1) + PR(T2)/C(T2) + ... + PR(Tn)/C(Tn) )

- T1...Tn are pages that link to A.
- C(Ti) is the number of outgoing links on Ti.
- d is the damping factor, usually 0.85, the probability that a user keeps following links; (1 - d) represents a random jump.

#### Notes
- It is computed iteratively until values converge.
- It can be seen as the probability that a random surfer lands on the page.
- It is used with many other factors (content relevance) to rank search results.

#### Example
If page A is linked by B (PR 1, 2 out-links) and C (PR 1, 1 out-link), then PR(A) = 0.15 + 0.85 × (1/2 + 1/1) = 1.425.

## Check yourself

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

1. What does PageRank measure?
   A. The loading speed of a page
   B. The number of words on a page
   C. The importance of a page based on the number and quality of pages linking to it
   D. The size of the web server
   Answer: C. A link is a vote and votes from important pages count more. (Key point: Meaning)

2. What does the damping factor d (usually 0.85) represent?
   A. The number of out-links
   B. The probability that a user keeps following links
   C. The number of pages on the web
   D. The loading delay
   Answer: B. (1 - d) is the chance of a random jump. (Key point: Damping factor)

3. Page A is linked by B (PR 1, 2 out-links) and C (PR 1, 1 out-link). What is PR(A)?
   A. 1.425
   B. 1.5
   C. 0.575
   D. 2.0
   Answer: A. PR(A) = 0.15 + 0.85 x (1/2 + 1/1) = 0.15 + 1.275 = 1.425. (Key point: Calculation)