Overview
A percentage shows a quantity as a part of 100. Percentages are commonly used for discounts, marks, statistics, interest and everyday comparisons.
Objective
Find a percentage of an amount, or express one quantity as a percentage of another.
What You Need
- A calculator or paper for working
- The percentage and/or amounts involved
Before You Start
Identify what the question is asking. For a percentage of an amount, convert the percentage to a decimal and multiply. To find what percentage one amount is of another, divide the part by the whole and multiply by 100.
How to Calculate
- Percentage of an amount: amount × percentage ÷ 100.
- Percentage one amount is of another: part ÷ whole × 100.
- Check that the answer makes sense compared with the original amount.
Worked Example
To find 25% of $80: 80 × 25 ÷ 100 = 20. So 25% of $80 is $20.
Useful Tips
- 10% is one tenth, so it is often easy to calculate mentally.
- 50% is one half and 25% is one quarter.
- Estimate first so calculator-entry mistakes are easier to spot.
Common Mistakes
- Using 25 instead of 0.25 when multiplying directly.
- Dividing the whole by the part instead of the part by the whole.
- Forgetting that a percentage is based on 100.
Important Notes
Percentages may be written as decimals or fractions. For example, 25% = 0.25 = 1/4.
FAQ
How do I turn a percentage into a decimal?
Divide by 100; for example, 18% becomes 0.18.
Can a percentage be more than 100%?
Yes. It means the quantity is greater than the reference amount.