Percentage of a Quantity
Multiply the quantity by the percent as a decimal.
Key idea
Multiply the quantity by the percent as a decimal.
In depth
To find p% of a number, convert to a decimal or fraction and multiply. Use 10% as a building block: 10% is one tenth, 5% is half of that.
Worked example
15% of 80 = 0.15 × 80 = 12. Or 10% = 8, 5% = 4, total 12.
Formula
Real-world uses
- Calculating a 15% tip, VAT on a purchase or the number of students who passed a test
Common mistake
Adding percentages across different bases, such as 20% off then 10% off is not 30% off.
How to learn this
- Read the key idea and say it in your own words.
- Work through the worked example, then try a similar problem.
- Use the interactive lesson’s visual and mini-quiz to check the pattern.
Frequently asked questions
What is Percentage of a Quantity?
Multiply the quantity by the percent as a decimal. It is a topic at the intermediate level in Arithmetic & Number Sense.
What is the formula for Percentage of a Quantity?
The key formula is p% of N = N × p/100.
Where is Percentage of a Quantity used in real life?
Real-world examples: Calculating a 15% tip, VAT on a purchase or the number of students who passed a test.
What should I learn before Percentage of a Quantity?
Make sure you are comfortable with Percentages, the previous topic in Arithmetic & Number Sense.
What is a common mistake with Percentage of a Quantity?
Adding percentages across different bases, such as 20% off then 10% off is not 30% off.
How can I practise Percentage of a Quantity?
Open the interactive lesson, play with the visual, then answer the three-question mini-quiz. Getting two right marks the topic complete.
What comes after Percentage of a Quantity?
Move on to Percentage Change next.
Related intermediate topics in Arithmetic & Number Sense
- Long Multiplication – Multiply by each digit of the multiplier, shift by place value, then add partial products.
- Long Division – Divide, multiply, subtract and bring down repeatedly to get the quotient.
- Factors and Multiples – Factors divide a number exactly; multiples are its products with whole numbers.
- Divisibility Rules – Quick tests: by 2 last digit even, by 3 digit-sum divisible by 3, by 5 ends 0/5, by 9 digit-sum divisible by 9.
- Prime Numbers – A prime has exactly two positive divisors: 1 and itself.
- Composite Numbers – Numbers greater than 1 with more than two factors.