Quick answer
A percent means per hundred. Learning a few mental shortcuts makes percentages easier to calculate.
Start with 10 percent
Divide by 10: 10% of 80 is 8. For 20%, double that result to get 16.
Find 1 percent
Divide by 100: 1% of 250 is 2.5. Then 5% is five times 2.5, or 12.5.
Use the general formula
Percent of a number = (percent ÷ 100) × number. So 15% of 60 = 0.15 × 60 = 9.
Worked examples
10% of 90 = 925% of 80 = 2015% of 60 = 9
Common mistake to avoid
Do not confuse 20% of 50 with 50% of 20; both happen to equal 10, but the quantities describe different bases.
Practice questions
Try these without looking at the answers first. Explain your reasoning aloud or write each step.
- Question:
10% of 130— Answer:13 - Question:
50% of 42— Answer:21 - Question:
20% of 75— Answer:15
What to learn next
Review the related lessons linked below, then practice independently. If you make an error, write down which rule you used and why it did not apply.