Solving questions involving ratios: How can we divide 35 blocks of chocolate in the ratio 4 : 3?
1
2 3
20
Add the parts to fi nd the total number of parts. e.g. 4 : 3 = 4 + 3 total parts = 7
Divide, to fi nd one part. e.g. 35 chocolate squares, one part = 35 ÷ 7 = 5
Multiply to fi nd the required share. e.g. 4 × 5 = 20 3 × 5 = 15 20 : 15
15
Simplifying ratios Consider the image shown. The ratio of frogs to penguins is 9 : 6
However, we can see that for every 3 frogs there are 2 penguins, so the ratio can also be written as 3 : 2
Ratios are generally written in simplest form. To simplify a ratio, fi nd the highest common factor (HCF) of the numbers and divide both sides by the HCF.
Sharing in a given ratio A ratio in the form 3 : 2 means that a quantity is divided into 5 parts (3 + 2) and then shared in such a way that the fi rst portion is 3
5 of the total and the second share is 2
Worked example 1 (i) Write the ratio 24 : 36 in its simplest form. (ii) Share €240 in the ratio 5 : 3.
(iii) Carol and Danielle shared some prize money in the ratio 2 : 3, respectively. Danielle got €360. How much did Carol get?
Solution (i)
(iii) 5 of the total.
(ii)
Section A Introducing concepts and building skills