Ratio: A ratio indicates how many times one number contains another. Thus, the ratio a is to b is the fraction 
In an inverse or reciprocal ratio, the original ratio is reciprocated.
Proportion: The equality of two ratios is known as proportion. If a:b = c:d, then it is expressed as a:b::c:d and say a, b, c and d are in proportion. The first and last terms are called extremes, while the middle terms are called means.
Formulae:
If 
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