Class 8 Maths - CBSE
Number Play
The chapter 'Number Play' (often aligned with Playing with Numbers in CBSE Class 8 Mathematics) introduces students to the fascinating world of numbers through puzzles, divisibility tests, and generalized forms of two-digit and three-digit numbers. It helps build a strong foundation in algebraic thinking by writing numbers in their expanded form, such as 10a + b. This chapter is vital for board exams as it tests logical reasoning and problem-solving skills. Questions from this chapter frequently appear in CBSE exams as 2-mark or 3-mark word problems and letter-arithmetic puzzles, making it a high-scoring section for attentive students.
Start Learning FreeKey Concepts
Generalized Form of Numbers
Any two-digit number can be written in expanded algebraic form as 10a + b, where 'a' is the tens digit and 'b' is the units digit.
Reversing Digits
When the digits of a two-digit number 10a + b are reversed, the new number becomes 10b + a.
Divisibility by 2, 5, and 10
A number is divisible by 2 if its last digit is even, by 5 if its last digit is 0 or 5, and by 10 if its last digit is 0.
Divisibility by 3 and 9
A number is divisible by 3 or 9 if the sum of all its individual digits is a multiple of 3 or 9 respectively.
Letter Puzzles (Cryptarithms)
Puzzles where letters take the place of digits in arithmetic operations, solved using logic and trial of single digits from 0 to 9.
Important Formulas
Board Exam Info
In CBSE Class 8 Mathematics, this chapter typically carries around 3 to 5 marks. Common question types include finding unknown digits in addition or multiplication puzzles (cryptarithms), proving divisibility rules using generalized forms, and solving word problems based on reversing the digits of a two-digit number.
Frequently Asked Questions
Why do we write numbers as 10a + b instead of just ab?
In algebra, writing 'ab' means 'a multiplied by b'. To represent a two-digit number where 'a' is the tens digit and 'b' is the units digit, we must use 10a + b.
How do I solve letter puzzles like A + B = C?
Test single-digit values from 0 to 9 for each letter. Remember that each letter must represent a unique digit, and the first digit of a multi-digit number cannot be 0.
Is the sum of a two-digit number and its reverse always divisible by 11?
Yes, because the sum equals 11(a + b), which is always a multiple of 11 regardless of the values of 'a' and 'b'.
Learn Number Play with Your AI Tutor
10 different ways to study this chapter. Free for 3 chapters per day.
Lecture
Key Points
Interactive
Quiz
Flashcards