Class 8 · Chapter 16

Playing with Numbers

General form of a number; divisibility tests; puzzles with digits.

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Tip: open the NCERT PDF for the original chapter text alongside the notes here.

Detailed theory

2, 3, 4, 5, 8, 9, 10, 11

— quick tests using digits. Enables mental checks.

Key concepts & formulas

Two-digit number:

10a + b

Three-digit number:

100a + 10b + c

Divisibility by

2

: last digit even.

Divisibility by

5

: last digit

0

5

Divisibility by

9

: sum of digits divisible by

9