Sharing in a given ratio
Lots of things in everyday life are shared in ratioA ratio is a way to compare amounts of something. It is usually written in the form a:b. . Money is shared, liquids are mixed and teams are assigned using ratios.
Drawing a table to represent the ratio can make these tasks easier.
Example
James and Helen get pocket money in the ratio \(3:5\). The total amount of pocket money they are given is 拢32. How much money do they each get?
The amount is divided into 8 equal parts since \(3 + 5 = 8\). Draw a rectangle with 8 sections and divide it in the ratio \(3:5\), labelling the two parts with the names James and Helen. Since James鈥 name comes first he gets three of the parts as the 3 is the first number in the ratio. Helen gets 5 parts, since her name is second.
Share the 拢32 between the 8 parts by dividing 32 by 8 and put the amount into each part of the diagram.
\(32 \div 8 = 4\)
| James (3) | Helen (5) | ||||||||
| 拢4 | 拢4 | 拢4 | 拢4 | 拢4 | 拢4 | 拢4 | 拢4 |
| James (3) | |
|---|---|
| 拢4 | |
| 拢4 | |
| 拢4 | |
| Helen (5) | |
| 拢4 | |
| 拢4 | |
| 拢4 | |
| 拢4 | |
| 拢4 |
The table shows that:
- James gets \(3 \times \pounds4 = \pounds12\)
- Helen gets \(5 \times \pounds4 = \pounds20\)
This can also be done when fractionA fraction is a part of a whole, for example 1/2. are involved.
Example
To make pink paint, red and white paint can be mixed in the ratio \(1:2\). If you need to make 4 litres of paint, how much red and white paint would you need?
The ratio has \(1 + 2 = 3\) parts.
4 divided by 3 = \(\frac{4}{3}\)
Each part is worth \(\frac{4}{3}\) litres.
| Red (1) | White (2) | |||
| \(\frac{4}{3}\) | \(\frac{4}{3}\) | \(\frac{4}{3}\) |
| Red (1) | |
|---|---|
| \(\frac{4}{3}\) | |
| White (2) | |
| \(\frac{4}{3}\) | |
| \(\frac{4}{3}\) |
Each part is worth \(\frac{4}{3}\) litres.
The table shows that:
- the amount of red paint needed is \(1 \times \frac{4}{3} = \frac{4}{3} \:\text{litres}\)
- the amount of white paint needed is \(2 \times \frac{4}{3} = \frac{8}{3} \:\text{litres}\)