Revision Notes for Class 7 Maths Chapter 6: Number Play

Quick revision notes summarizing all key concepts from Class 7 Maths Chapter 6 “Number Play”. These Class 7 Mathematics Chapter 6 notes are ideal for quick revision just before exams.

• Parity refers to whether a number is odd or even.
• Sum rules: Even+Even=Even, Odd+Odd=Even, Even+Odd=Odd. Subtraction follows the same rules as addition for parity purposes.
• An odd count of odd numbers sums to odd; an even count of odd numbers sums to even. Any count of even numbers always sums to even.
• Product parity: a product is even if at least one factor is even; a product is odd only if both factors are odd.
• All even numbers can be written as 2n; all odd numbers can be written as 2n − 1 (n = 1, 2, 3, …).
• A classic 3×3 magic square using numbers 1–9 has magic sum 15 and is unique up to rotation/reflection (8 total variations). For a magic square with centre value m, every row/column/diagonal sums to 3m.
• Adding a constant c to every cell of a magic square increases the magic sum by 3c; multiplying every cell by k multiplies the magic sum by k.
• The Chautisa Yantra is a famous 10th-century 4×4 magic square from Khajuraho with magic sum 34, where even the four corners, four central cells, and any 2×2 block sum to 34.
• The Virahanka-Fibonacci sequence (1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, …) is formed by adding the two previous terms; its parity repeats in a 3-term cycle: odd, odd, even.
• The number of ways to write n as an ordered sum of 1s and 2s equals the Virahanka term for n (e.g., 6 can be written in 13 ways).
• Cryptarithms are puzzles where letters represent digits in an arithmetic equation; solve them using place-value reasoning and testing constraints systematically.

NCERT Solutions: Class 7 Maths Chapter 6
Extra Questions: Class 7 Maths Chapter 6

For the full chapter, see the Class 7 Maths book page and the Class 7 Maths Formulas Handbook.

Written by Satish

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