Definitions and Formulas

Direct Proportion
In direct proportion, when one quantity increases/decreases, the other quantity will follow suit. Hence the two quantities are always in the same ratio. 

If y is directly proportional to x, then y = kx, where k is a constant and k ≠ 0 
 y1/x1 = y2/x2, where (x1, y1) and (x2, y2) are any two pairs of values of x and y. 

Inverse Proportion
In inverse proportion, when one quantity increases, the other quantity decreases and vice versa. However, the product of the two quantities is a constant. 

If y is inversely proportional to x, then y = k/x, where k is a constant and k ≠ 0.
x1, y1 = x2, y2, where (x1, y1) and (x2, y2) are any two pairs of values of x and y. 

Worked Examples

View the following:

Worked Example 2

View the following: