- Method A
Calculate 10% giving £3. Halve this to get 5% which is £1.50.
- Adding 10% and 5% gives us 15% so £3 + £1.50 = £4.50 which is 15% of £30.
- Method B: The unitary method
- Find 1% of £30 which is £0.30 or 30p.
- Multiplying 1% by 15 gives us 15% and so 0.30 × 15 is £4.50.
Informal Methods
Let's use the example 11% of £240.
- Calculating 10% of £240 gives us £24
- Dividing 10% by 10 gives 1% so £24 ÷ 10 = £2.40.
- 11% of £240 is £24 + £2.40 = £26.40
As you can see any of these methods work. It's up to you which you prefer.
There's an exercise
here for you to practise finding percentages that you might like to try.
Solving problems using percentage changes
Example: There is a discount of 25% in a sale. Jane paid £15 for a skirt in the sale
what was its original price?
Method A: Using inverse operations.
Let's say that p is the original price.
Then, p × 0.75 = £15
So p = 15 ÷ 0.75 = £20
Method B: Unitary method
- £15 is 75%
- so £15 ÷ 75 = £0.20 is 1%
- so £20 is 100%.
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