RATIO AND PROPORTION

Ratio :-  When the relation between two quantities of the same kind is indicated by division or a fraction then the relation is called ratio.
For eg.  ratio of 8m to 4m is
                                $\frac{8}{4}$   or   $\frac{2}{1}$   or  2:1
               Here,  2 is called antecedent and 1 is consequent.
Note:-  A ratio has no units in itself.

Proportion:-  A proportion is defined as a statement which shows that two ratios are equal.
                     If  a:b=c:d, then we say that a, b, c and d are in proportion
               Here,  a and b are called extreme terms.
                          b and c are called middle terms or means.
                          d is called fourth proportional to a, b and c.
Note:-  a:b=c:d is also written as a:b::d  or  $\frac{a}{b}=\frac{c}{d}$.

Condition for Proportionality:-  If a, b, c and are in proportion then
                                                    $\frac{a}{b}=\frac{c}{d}$
                                             or     ad = bc
Note:-  In a proportion the product of the extreme terms is equal to the product of the means(middle) terms.

If a:b::c:d, then d is called the fourth proportion to a, b, c.
If a:b::b:c, then c is called the third proportion to a, b.
Mean proportion between a and b = $\sqrt{ab}$
If a:b::b:c or  $\frac{a}{b}=\frac{c}{d}$  or  $a\times c=b\times b$  or $ac=b^{2}$
        Then, a, b and c are in continued proportion.

Duplicate Ratio of (a:b) is $(a^{2}:b^{2})$.
Sub Duplicate ratio of (a:b) is $(\sqrt{a}:\sqrt{b})$.
Triplicate ratio of (a:b) is $(a^{3}:b^{3})$.
Sub Triplicate ratio of (a:b) is $(a^{\frac{1}{3}}:b^{\frac{1}{3}})$.

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