Finding a Percentage of a Number
Finding a percentage of a number is one of the most practical maths skills there is. It tells you exactly how much a part of something is — whether that is a discount, a test score, or a tax amount.
The Core Formula
Percentage of a number = (Percentage / 100) times the Number.
Or: convert the percentage to a decimal, then multiply.
Simple Method – Decimal Multiplier
Convert the percentage to a decimal (divide by 100), then multiply by the number.
Find 30% of 200
30 / 100 = 0.30. 0.30 times 200 = 60.
Find 15% of 80
15 / 100 = 0.15. 0.15 times 80 = 12.
Find 7.5% of 400
7.5 / 100 = 0.075. 0.075 times 400 = 30.
Building Block Method
Break the percentage into easy parts using 10%, 1%, and 5%.
Find 35% of 260
10% of 260 = 26. 30% = 3 times 26 = 78. 5% = half of 26 = 13. 35% = 78 + 13 = 91.
Find 17.5% of 120
10% = 12. 5% = 6. 2.5% = 3. 17.5% = 12 + 6 - 0.5... Actually: 10% + 5% + 2.5% = 12 + 6 + 3 = 21.
Handy Reference Table
| Percentage | Multiplier | Quick Method |
|---|---|---|
| 10% | 0.1 | Divide by 10 |
| 1% | 0.01 | Divide by 100 |
| 5% | 0.05 | Half of 10% |
| 25% | 0.25 | Divide by 4 |
| 50% | 0.5 | Divide by 2 |
| 75% | 0.75 | Three-quarters |
| 20% | 0.2 | Divide by 5 |
Real-Life Examples
- VAT at 20% on a £350 item: 0.2 times 350 = £70 tax.
- A 15% tip on a £46 meal: 0.15 times 46 = £6.90.
- A student needs 60% to pass. The test is out of 75: 0.6 times 75 = 45 marks needed.
Key Takeaways
- Convert the percentage to a decimal, then multiply by the amount.
- Use the building-block method (10%, 5%, 1%) for mental maths.
- The answer is always in the same units as the original number.
- Check: your answer should be smaller than the original when % is less than 100.
Practice Questions
- Find 40% of 150.
- Find 12% of 250.
- Find 8.5% of 600.
- A coat costs £180 and has a 35% discount. How much is the discount?
- A recipe uses 600 g of flour. You want 75% of the recipe. How much flour do you need?