Topics covered within this unit: 10.1 Ratio and proportion 10.2 Scaling
The Learning Outcomes covered in this unit are contained in the following sections:
N.2b GT.2a
Key words Ratio
Direct proportion Scaling Scale Scale diagram
Ratio, proportion and scaling
Something to think about …
Unit Intro Text
Scale drawings are based on the geometric principle of similarity. Two fi gures are similar if they have the same shape, even though they may have diff erent sizes.
You are asked to make a scale drawing of a campground. The picnic area is a rectangle and has a length of 44 metres and a width of 21 metres in real life.
Draw a scale diagram of this picnic area using a suitable scale.
10.1 Ratio and proportion
By the end of this section you should: ● understand what a ratio is ● be able to divide amounts in a given ratio ● understand direct proportion ● be able to solve problems using direct proportion
Ratio A ratio is a relationship between two amounts.
Ratios show how much of one thing there is compared to another. When we express ratios in words, we use the word ‘to’ – we say, ‘the ratio of something to something else’. In Maths, we replace the word ‘to’ with a colon (:).
In the picture to the left: The ratio of red sweets to yellow sweets is 3 : 5 The ratio of red sweets to blue sweets is 3 : 7 The ratio of blue sweets to yellow sweets is 7 : 5