Ratio, Proportion and it's Properties

In general, four numbers are said to be in proportion, if the ratio of the first two quantities is equal to the ratio of the last two. In general, the symbol for representing a proportion is “: :” (i) The numbers a, b, c and d are in proportional if the ratio of the first two quantities is equal to the ratio of the last two quantities, i.e., a : b : : c : d and is read as ‘a is to b is as c is to d’. The symbol ‘ : : ‘ stands for ‘is as’. (ii) Each quantity in a proportion is called its term or its proportional. (iii) In a proportion; the first and the last terms are called the extremes; whereas the second and the third terms are called the means.