The principle behind scale drawings in simple: we decide on a length on the paper to represent a length in real life.

So if we wanted a scale drawing of a room, we might choose to represent 1m by 1cm. Alternatively, if the room was particularly big, we could choose to represent 2m by 1cm.

**Examples**

As studying scale drawings is a very practical matter, it is best “learned by doing”. To do the following exercise you will need a ruler and your textbook.

**Exercise**

Let’s complete exercise 15F on page 245 of the textbook:

The answers are below:

**Scales as ratios**

It is often useful to write a scale without any units in it. For instance, because 1m=100cm, if we have a scale of 1cm to represent 2m, we can write this as:

1cm : 2m = 1cm : 200cm. Because the units are the same, we now don’t need to write them, i.e. the scale will apply for any units. So we can just write the scale as 1:200.

Also, remember that 1km = 1000m (and as 1m = 100cm, so therefore 1km = 100,000cm)

**Example**

**Exercise**

Let’s complete exercise 15G on page 246 of the textbook:

The answers are below: