Class 8 Maths - CBSE
A Story of Numbers
A Story of Numbers in Class 8 Mathematics takes students on a fascinating journey through the evolution and properties of numbers. This chapter builds a strong foundation in number theory by exploring number puzzles, divisibility rules for 2, 3, 5, 9, and 10, and writing numbers in generalized form using algebraic expressions like 10a + b. Understanding how numbers behave under arithmetic operations is crucial for mental math and algebraic problem-solving. While this is often an introductory chapter, it carries about 3 to 5 marks in CBSE Class 8 exams through puzzle-based word problems and divisibility test questions.
Start Learning FreeKey Concepts
Numbers in Generalized Form
A two-digit number like ab can be written in its expanded algebraic form as 10a + b, where a is the tens digit and b is the units digit.
Divisibility by 10
A number is divisible by 10 if its units digit is 0, meaning the last digit of the number must be zero.
Divisibility by 5
A number is divisible by 5 if its units digit is either 0 or 5, making it easy to identify multiples of 5.
Divisibility by 2
A number is divisible by 2 if its units digit is an even number (0, 2, 4, 6, or 8).
Divisibility by 3 and 9
A number is divisible by 3 (or 9) if the sum of its digits is a multiple of 3 (or 9).
Important Formulas
Board Exam Info
This chapter typically carries around 3 to 5 marks in CBSE Class 8 Mathematics examinations. Common question types include finding unknown digits in addition or multiplication puzzles, checking divisibility of large numbers, and solving word problems based on reversing the digits of a two-digit or three-digit number.
Frequently Asked Questions
Why do we write numbers like 10a + b instead of just ab?
Writing ab looks like a multiplied by b in algebra. Writing 10a + b shows the actual place value, where a is in the tens place and b is in the units place.
How do I solve letter puzzles like AB + BC = CCC?
Start by analyzing the units column to find relationships between the letters, then test possible single-digit values from 0 to 9 that satisfy the addition equation.
Is a number divisible by 6 if it is divisible by 2 and 3?
Yes! Since 2 and 3 are coprime numbers, any number that is divisible by both 2 and 3 will always be divisible by 6.
Learn A Story of Numbers with Your AI Tutor
10 different ways to study this chapter. Free for 3 chapters per day.
Lecture
Key Points
Interactive
Quiz
Flashcards