# How are scales and ratios related?

May 30, 2018

A scale is always in the form $1 : n$

A ratio compares two or more quantities.

#### Explanation:

A scale is a specific type of ratio.

It compares a unit on a map or plan or on a scaled model to an actual distance on a map or the size of a real object.

A scale is given in the form: $\text{ "1" ":" } n$

On a map, a scale of $\text{ "1:50" }$ means

$\text{ } 1 c m$ on the map represents $50 c m$ on the ground (in reality)

or $\text{ "200mm" }$ on a plan to this scale, indicates a length of
$200 \times 50 = 10 , 000 m m$ in reality.

A ratio is a comparison between two or more quantities of the same type.

e.g: girls : boys are in the ratio $4 : 3$ means that:

for every $4$ girls there are $3$ boys.

If there are $35$ children in a class with this ratio, we have:

$\frac{4}{7}$ of the class are girls (which means $\frac{4}{7} \times 35 = 20$ girls.)

$\frac{3}{4}$ of the class are boys (which means $\frac{3}{7} \times 35 = 15$ boys.)