# Direct Proportion and Indirect Proportion

Posted in Terms Defined

Two quantities x and y are said to be in direct proportion if they increase (decrease) together in such a manner that the ratio of their corresponding values remains constant. That is if $$\frac{x}{y} = k$$ [ k is a positive number], then x and y are said to vary directly. In such a case if $$y_1, y_2$$ are the values of y corresponding to the values $$x_1, x_2$$ of a respectively then $$\frac{x_1}{y_1} = \frac{x_2}{y_2}$$.

Two quantities x and y are said to be in inverse proportion if an increase in x causes a proportional decrease in y (and vice-versa) in such a manner that the product of their corresponding values remains constant. That is, if $$xy = k$$, then x and y are said to vary inversely. In this case if $$y_1, y_2$$ are the values of y corresponding to the values of x respectively then $$x_1y_1 = x_2y_2$$ or $$\frac{x_1}{x_2} = \frac{y_2}{y_1}$$.