What is proportion?
A proportion is formed when two ratios are equal, such as 2 : 3 = 4 : 6. We use proportion to work out an unknown amount when things grow at the same rate — for example when buying more of the same item, or making a bigger batch of a recipe. If one amount doubles, the other doubles too.
Using proportion
The easiest way is to first find the value of one unit, then multiply for the number you need. This is called the unitary method, and it works for money, mass, length and many other everyday amounts.
Key idea
Cost of many = cost of one × number of items. Find one first, then scale up.
Worked example
If 2 pencils cost RM4, how much do 6 pencils cost?
Cost of 1 pencil = RM4 ÷ 2 = RM2.
Cost of 6 pencils = RM2 × 6 = RM12.
Remember
- Find the value of one unit first.
- Then multiply for the amount you need.
- Keep the same units (RM, kg, km).