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Chapter 5: Number Play Notes

Home / Class Notes / class 8 / Mathematics / Chapter 5: Number Play
✓ Free notes class 8 Mathematics 1 study file

About these notes

Class 8 Mathematics Chapter 5 Number Play notes give clear definitions, prime-factor methods, worked examples and quick revision for CBSE and Bihar Board students. Main sub-topics: prime and composite numbers (अभाज्य संख्या / भाज्य संख्या), divisibility tests (2, 3, 5, 9, 11), prime factorisation and trees, finding HCF (महत्तम समापवर्तक) and LCM (लघुत्तम समापवर्त्य) from factors, and shortcut rules like HCF × LCM = product for two numbers. Use these notes with chapter tests and mock tests on Merit Spring ROH to practise important questions, try MCQ rounds and check question answer steps while revising for school exams.

Key points you will learn

  • Class 8 Mathematics Chapter 5 Number Play: notes on prime/composite (अभाज्य संख्या/भाज्य संख्या), factors (गुणक) and multiples (गुणज)
  • Divisibility tests: last digit for 2 and 5; sum of digits for 3 and 9; alternating sum for 11; last two digits for 4
  • Prime factorisation examples and trees, e.g. 2³ × 3² × 5 shown as prime factors
  • Find HCF by product of common primes with smallest powers; LCM by product of all primes with highest powers
  • Relation for two numbers: HCF × LCM = product of the numbers and LCM = (a × b) ÷ HCF
  • Tips: write prime factors instead of trial division, mark common factors, and remember 1 is neither prime nor composite
  • Quick exam tip: show prime factorisation steps to get full method marks and practice timed MCQ drills

What is inside this chapter

📄

Number Play - Chapter 5 Notes (Class 8 Maths)

Class 8 Maths Number Play - Chapter 5 handwritten-style revision notes for CBSE and Bihar Board students.

📥 Open notes

Questions students ask

How to use these notes for quick revision?

Start by memorising divisibility rules and main definitions, then practise 2–3 worked examples from prime factor trees and HCF/LCM. Finish with a timed chapter test on Merit Spring ROH to spot weak steps and improve speed.

Where can I find Class 8 Maths Chapter 5 Number Play important questions and MCQ?

Find important questions and MCQ linked from the chapter notes page on Merit Spring ROH and in the chapter test and mock test sections; use the note examples to check your question answer steps.

How do I find HCF and LCM using prime factorisation?

Write prime factors of each number, take common primes with smallest powers for HCF and take all primes with highest powers for LCM; use the rule HCF × LCM = product for two numbers to verify results.

What is the difference between prime and composite numbers?

A prime number (अभाज्य संख्या) has exactly two distinct positive factors: 1 and itself. A composite number (भाज्य संख्या) has more than two positive factors. The number 1 is neither prime nor composite.

How can I speed up divisibility checks in exams?

Memorise the simple tests (2, 3, 5, 9, 11, 4) and practise applying them quickly on 2–3 digit numbers; for larger numbers use digit-sum shortcuts and split the number into chunks to reduce calculation time.

← Previous chapter Chapter 4: Quadrilaterals

More Mathematics chapters

Chapter 1: A Square and a Cube Chapter 2: Power Play Chapter 3: A Story of Numbers Chapter 4: Quadrilaterals Chapter 6: We Distribute Yet Things Multiply Chapter 7: Proportional Reasoning 1 All chapters →

class 8 — other subjects

ENGLISH Social Science Science