# 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 and b and c are called mean terms. The product of mean in the ratio are equal to product of extremes. Two ratio are either 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 Examples

Question 1: 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

#### Practise This Question

The effect of today's radioactive fallout problem will be expressed in the population after few generations because: