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**Ratio** – the ratio of two quantity a & b in the same unit is the fraction $\frac{a}{b}$ and we write it a:b

In a ratio a:b we call a as the first term or antecedent and b the second term or consequent.

**Rule**– the multiplication or division of each term of a ratio by the same non zero number does not effect the ratio.

Example

4:5 = 8:10= 12:15, also 12:15 = 8:10

**Proportion**– the quantity of two ratios is called proportion

a:b = c:d we write a:b ::c:d and we say that a,b,c, d, are in proportion. Here a and d are called extremes while b & c are called mean term

Product of means = product of extreme

Thus a:b::c:d

(b×c) = (a×d)

**Third proportion**

If a:b=b:c, then c is called the third proportion to a & b.

4:8::8:16 – 16 is called third proportion.

**Continued proportion** e.g. 4:3::8:16

**Forth proportion**

If a:b = c:d then d is called the fourth proportion to a,b,c

**Mean proportion**–

Mean proportion between a & b is $\sqrt{ab}$

4:2::8:16 or 82 = 4×16

8 is mean proportion.

**Comparison of ratio**

a:b>c:d

$\frac{a}{b}> \frac{c}{d}$

**Compound ratio**– duplicate ratio a:b is $(a^2:b^2)$

**Sub duplicate ratio**– a:b is $(\sqrt{a}:\sqrt{b})$

**Triplicate ratio** – a:b is $(a^3:b^3)$

**Sub triplicate ratio**– a:b is $a^\frac{1}{3}:b^\frac{1}{3}$

If, $\frac{a}{b} = \frac{c}{d}$

then $\frac{a+b}{a-b} = \frac{c+d}{c-d}$

Verification:-

1) We say that x is directly proportional to y, if x= ky for some constant K

then we write $x\propto y$

2) We say that x is inversely proportional to y, if xy = k for some constant K

then we write $x\propto 1/y$