# What is a proportion? How to use it and what situation to use it in?

Aug 29, 2017

A proportion is a ratio of two values that is maintained constant.

#### Explanation:

A proportion is a ratio of two values that is maintained constant.
If one part of the ratio changes, the other one changes similarly. This is commonly expressed as fractions.

For example, $\frac{5}{2}$ is a proportion. To maintain the same proportion when one of the values changes, the other value must change in the same way. If we change the ‘5’ to a ‘10’, we must change the ‘2’ to a ‘4’ (both values multiplied by 2) to maintain the proportion.

This becomes very useful in everyday life! We use it to make “scale drawings” and models for larger constructions and devices. We can use it to “scale” up or down a set of dimensions. It is a cornerstone of geometric and trigonometric calculations used in innumerable applications.

A common household use is in adjusting food recipes for different sizes of diners. A recipe “designed” for four people can be “scaled” for any other number by applying the proportion to the recipe ingredients.