What is a ratio?
A ratio shows how much of one thing there is compared to another.
Ratios are usually written in the form:
a:b
If you are making orange squash and you mix one part orange to four parts water, then the ratio of orange to water will be 1:4 (1 to 4).
The order in which a ratio is stated is important. Changing the order of the numbers in a ratio changes the proportions.
Watch: Ratios
Narrator: To make a purple dinosaur, we use a ratio of 2:3. That's two blue dinosaurs for every three red dinosaurs.
Uh, hey! We need that!
And what if we want to make an even bigger purple dinosaur and use eight blue dinosaurs instead of two? How many red dinosaurs will we need then?
So, eight is two times four. And to keep the same ratio, we can multiply the three red by four as well, which makes 12.
8:12 is the same ratio as 2:3, but it's much bigger. Four times bigger!
Uh oh! Time to go!
How to simplify ratios
The ratio of red to blue dinosaurs is 12:18.
This ratio can be simplified. Both 12 and 18 can be divided by 2.
12 ÷ 2 = 6
18 ÷ 2 = 9
So a simpler way to write 12:18 is 6:9.
12:18 = 6:9
The ratio can be made simpler again, if we divide by 3.
6 ÷ 3 = 2
9 ÷ 3 = 3
So an even simpler way to write 12:18 is 2:3.
12:18 = 2:3
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Primary maths teaching resources
Visit BBC Bitesize for Teachers to see videos, activities and more resources to use in maths classes for KS1 and KS2.
More on Processes in mathematics
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