Percentage of an amount
You learn to work out a percentage of a number, and what something costs after a discount.
How to work it out
- Write down the whole number: that is 100%.
- Divide by 2 for 50%, by 4 for 25% and by 10 for 10%.
- Build the requested percentage from these parts: 75% is 50% + 25%, 5% is half of 10%.
- For a discount, subtract that amount from the price.
310
A worked example
25% of 40
- Write 40 as 100%.
- Divide by 4 for 25%: 40 ÷ 4 = 10.
- It is 10.
14
More examples
75% of 80
- Divide by 2 for 50%: 80 ÷ 2 = 40.
- Divide by 4 for 25%: 80 ÷ 4 = 20.
- Add them: 40 + 20 = 60.
- It is 60.
34
£240 with a 15% discount
- Divide by 10 for 10%: 240 ÷ 10 = 24.
- Take half for 5%: 24 ÷ 2 = 12.
- The discount is 24 + 12 = 36.
- Take it away: 240 − 36 = 204.
- It costs £204.
Try it yourself
20% of 300
10% of 40
Watch out
You work out 25% by dividing by 25: 40 ÷ 25.
25% is a quarter. Divide by 4, not by 25.
You work out the discount and forget to take it away: £80 with a 25% discount becomes £20.
Read the question again: what does it cost now? Take the discount away from the price.
Tips
- For 5% take half of 10%.
- For a discount, take the amount away from the price.
Why it works
With 100, 50, 25 and 10 percent you have four easy pieces: the whole, the half, a quarter and a tenth. You build every other percentage from those, like 75% is 50% + 25%. That is easier than thinking of a new calculation each time.