# Proportion Formula

An equation is said to be in proportion when the elements in it, say, a, b, c and d are in proportion. a and d are called extremes, whereas b and c are called mean terms. The product of means in the ratio is equal to the product of extremes. Two ratios are said to be equal if their cross products are equal.

The Proportion Formula is given as,

$\large a:b::c:d\Rightarrow \frac{a}{b}=\frac{c}{d}$

### Solved Example

Question: What is the value of x in 6 : x :: 2 : 5?

Solution:

6 : x :: 2 : 5
6 : x = 2 : 5

$\frac{6}{x}$ = $\frac{2}{5}$

6 $\times$ $\frac{5}{2}$ = x

x = 6 $\times$ $\frac{5}{2}$

x = $\frac{30}{2}$

x = 15