Class 6 · Chapter 12

Ratio and Proportion

Concepts of ratio and proportion; unitary method.

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Detailed theory

Comparison of two like quantities using division. Ratio of

a

b

is written

a:b

a/b

. E.g. ratio of

6

boys to

9

girls is

6:9 = 2:3

in lowest form.

Key concepts & formulas

A ratio compares two quantities of the same kind:

a : b = \dfrac{a}{b}

In ratio

a:b

, order matters.

Four numbers are in proportion if

a:b :: c:d

, i.e.,

ad = bc

In the unitary method, first find the value of one unit, then scale.

Continued proportion:

a:b :: b:c \Rightarrow b^2 = ac