Ratio and Proportion

 ·       Ratio is nothing but comparison of quantities.
·       A proportion is a name we give to a statement that two ratios are equal.

It can be written in two ways:
·       Two equal fractions, 
or
·       Using a colon,    a:b = c:d

·       When two ratios are equal, then the cross products of the ratios are equal.
·       That is, for the proportion, a:b = c:d ,  a x d = b x c

Example:
If  A:B = 2:3 & B:C = 5:7 , then A:B:C = ?

            A:B:C= 10:15:21

Points to Remember:
            a : b : :  c : d
            a : b  =  c : d
               ad  = bc
·       Fourth Proportion d = bc/a
·       Third Proportion c = b2/a

·       Second Proportion b = Mean Proportion = √ca
·       There is no formula for First Proportion ,Hence no question would be asked based on first proportion.
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