Skip to main content
Super TutorResources
Chapter 3 of 8
QuestionsNotesFlashcardsSummaryFormulasQuizConceptsSyllabusPlan
Revision Notes

The World of Numbers

CBSE · Class 9 · Mathematics

Quick revision notes for The World of Numbers — CBSE Class 9 Mathematics. Key concepts, formulas, and definitions for last-minute revision.

89 questions76 flashcards5 concepts

Interactive on Super Tutor

Studying The World of Numbers? Get the full interactive chapter.

Quizzes, flashcards, AI doubt-solver and a step-by-step study plan — built for revision notes and more.

Try Super Tutor — Free

1,000+ Class 9 students started this chapter today

Key Topics to Revise

1

1. Growth of Number Systems

  • Natural numbers are the counting numbers {1, 2, 3, 4, ...}.
  • Natural numbers came from one-to-one correspondence in counting objects.
  • Natural numbers are closed under addition.
2

2. Zero and Integers

  • Zero was formally transformed into a number by Brahmagupta in 628 CE in the Brāhmasphuṭasiddhānta.
  • The chapter summary gives Brahmagupta's formalisation of zero as 629 CE.
  • Brahmagupta defined zero as a - a = 0.
3

3. Rational Numbers

  • Rational numbers are denoted by Q for quotient.
  • A rational number can be written in the form p/q where p and q are integers and q is not zero.
  • Rational numbers include integers, whole numbers, and fractions.
4

4. Irrational Numbers

  • Irrational numbers cannot be written as a ratio of integers.
  • Irrational numbers have non-terminating, non-repeating decimal expansions.
  • Baudhāyana composed the Shulbasūtra around 800 BCE and encountered lengths that defied fractions.

Get complete notes with diagrams and examples

Full Notes

Key Concepts

Natural numbers are the counting numbersThe Lebombo Bone has 29 notchesZero became a formal operational numberIntegers are the set {The basic rules are a +

Frequently Asked Questions

What are the important topics in The World of Numbers for CBSE Class 9 Mathematics?
The World of Numbers covers several key topics that are frequently asked in CBSE Class 9 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.
How to score full marks in The World of Numbers — CBSE Class 9 Mathematics?
Understand the core concepts first, then work through the 89 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

More resources for The World of Numbers

All 8 chapters — CBSE Class 9 Mathematics Revision Notes

For serious students

Get the full The World of Numbers chapter — for free.

Quizzes, flashcards, AI doubt-solver and a step-by-step study plan for CBSE Class 9 Mathematics.

Try Super Tutor Free
Try the full chapter — Free