Class 6 · Chapter 3

Playing with Numbers

Factors and multiples; prime and composite numbers; divisibility rules; HCF and LCM.

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Detailed theory

A factor of a number divides it exactly (no remainder). A multiple is the product of a number with a natural number.

1

is a factor of every number; every number is a multiple of

1

and itself.

Key concepts & formulas

A prime number has exactly two factors:

1

and itself.

1

is neither prime nor composite.

\text{HCF}(a,b) \times \text{LCM}(a,b) = a \times b

Divisibility by

3

: sum of digits divisible by

3

Divisibility by

9

: sum of digits divisible by

9