Percentage of an Amount
To find a percentage of an amount without a calculator, split the percentage into easy chunks. Useful chunks include 10%, 5%, 1%, 50% and 25%. Find the chunks you need, then add or subtract them to make the required percentage.
Common mistake: Remember that 5% is half of 10%, not 5 less than 10%. Always work with the amount you are finding the percentage of.
Worked example:
Find 15% of £80 without a calculator.
- Step 1Split 15% into 10% and 5%.\[10\% \text{ of } 80 = 8\]
- Step 25% is half of 10%.\[5\% \text{ of } 80 = 4\]\[8 + 4 = 12\]
Answer:
15% of £80 is £12.
Worked example:
Find 35% of 240 without a calculator.
- Split 35% into 30% and 5%.\[10\% \text{ of } 240 = 24\]\[30\% \text{ of } 240 = 3 \times 24 = 72\]\[5\% \text{ of } 240 = 12\]\[72 + 12 = 84\]
Answer:
35% of 240 is 84.