Class 7 Maths - WEST-BENGAL
Number Play
The Chapter 'Number Play' in the Class 7 Mathematics syllabus under the West Bengal Board of Secondary Education (WBBSE) introduces students to fascinating patterns and properties of numbers. This chapter focuses on puzzle-solving, divisibility tests, magic squares, and playing with digits of numbers like two-digit and three-digit numbers. It helps build a strong foundation in mental math and logical reasoning. For board exams, questions from this chapter test the student's analytical skills through word puzzles, algebraic representation of numbers, and finding hidden patterns, making it a scoring yet conceptually rich topic.
Start Learning FreeKey Concepts
General Form of a 2-Digit Number
A two-digit number with tens digit 'a' and units digit 'b' can be written algebraically as 10a + b.
Reversing Digits of a Number
When the digits of a two-digit number 10a + b are reversed, the new number becomes 10b + a.
Divisibility by 9 and 3
A number is divisible by 9 (or 3) if the sum of its digits is a multiple of 9 (or 3).
Divisibility by 11
A number is divisible by 11 if the difference between the sum of digits at odd places and even places is either 0 or a multiple of 11.
Magic Squares
A grid of numbers where the sum of numbers in each row, column, and both diagonals is always the same.
Important Formulas
Board Exam Info
In the West Bengal (WBBSE) Class 7 final examinations, 'Number Play' typically carries around 4 to 6 marks. Common question types include finding unknown digits in arithmetic puzzles (cryptarithms), proving divisibility rules, solving word problems based on reversing digits, and completing magic squares.
Frequently Asked Questions
Why do we write 2-digit numbers as 10a + b instead of ab?
In algebra, writing 'ab' means 'a multiplied by b'. To represent the actual value of a number where 'a' is the tens digit and 'b' is the units digit, we must write it as 10a + b.
How do I solve puzzle questions where letters replace digits?
Look at the units column first to find clues about possible digit values, keeping in mind that each letter represents a single digit from 0 to 9, and the first digit of a number cannot be 0.
Are the divisibility rules mandatory for solving these puzzles?
Yes, knowing shortcuts like divisibility by 3, 9, and 11 helps you quickly check your answers and solve complex number puzzles without doing long divisions.
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