A **tape diagram** is another way to represent a ratio. All the parts of the diagram that are the same size have the same value.

For example, this tape diagram represents the ratio of ducks to swans in a pond, which is $4:5$.

The first tape represents the number of ducks. It has 4 parts.

The second tape represents the number of swans. It has 5 parts.

There are 9 parts in all, because $4+5=9$.

Suppose we know there are 18 of these birds in the pond, and we want to know how many are ducks.

The 9 equal parts on the diagram need to represent 18 birds in all. This means that each part of the tape diagram represents 2 birds, because $18\div9 = 2$.

There are 4 parts of the tape representing ducks, and $4 \boldcdot 2=8$, so there are 8 ducks in the pond.