Find a fraction of a quantity by dividing by the denominator and multiplying by the numerator, then use it in problems. It is a Foundation topic, aimed at grade 2. Free questions with answers are on this page. Worked examples show each line before you try the questions.
Finding a fraction of an amount is divide by the bottom, multiply by the top. 53 of 45 is 45÷5=9, then 9×3=27. The 'of' is a multiply, so you can also write 53×45. Divide first when the numbers are friendly, because 45÷5 is nicer than multiplying 3×45 and then dividing by 5.
If a fraction of something is used up, the rest is 1 minus that fraction, then that fraction of the original amount. With two groups, find each amount (or add the fractions first) and subtract from the total. Both routes must agree.
Keep the units. 87 of 640 g is 560 g, not 560. And do not stop after the divide: one eighth is a stepping stone, not the answer, unless the question asked for 81.
Objectives
The denominator says how many equal parts.
3/5 is three of those parts.
3/5 of 40 is the same as 40 × 3 ÷ 5.
Key points
Find a unit fraction of an amount, e.g. 51 of 45.
Find any fraction of an amount, e.g. 53 of 45.
Find the amount that is left after a fraction has been used.
Solve two-step problems where two different fractions of the same total are given.
Worked examples
Example 1
Work out 1/5 of 35.
2 marks
Divide 35 by 5.
35 ÷ 5 = 7.
The result is 7.
Answer: 7
Common slips
Slip: Multiply 5 by 35. That is a different operation, so it answers a different question.
Slip: 35 × 5 = 175. That uses multiplication, but this step needs division.
Slip: The result is 11. That does not match the working above it.
Example 2
Work out 3/4 of 24.
2 marks
24 ÷ 4 = 6.
6 × 3 = 18.
The result is 18.
Answer: 18
Common slips
Slip: 24 × 4 = 96. That uses multiplication, but this step needs division.
Slip: 6 + 3 = 9. That uses addition, but this step needs multiplication.
Slip: The result is 22. That does not match the working above it.
Example 3
A class has 30 pupils. 2/5 of them walk to school. How many pupils walk to school?
3 marks
30 ÷ 5 = 6.
6 × 2 = 12.
The result is 12.
Answer: 12
Common slips
Slip: 30 × 5 = 150. That uses multiplication, but this step needs division.
Slip: 6 + 2 = 8. That uses addition, but this step needs multiplication.
Slip: The result is 16. That does not match the working above it.
Questions and answers
GCSE Maths fractions of an amount questions and answers. Try each one, then open the answer. Easy questions come first.
Question 1 Easy2 marks
Find 3/5 of 20.
Show answer
Answer: 12
1/5 of 20 comes first.
Then multiply by 3.
M1 — 1/5 of 20 comes first.
A1 — Answer 12
Question 2 Easy2 marks
Find 1/6 of 18.
Show answer
Answer: 3
Divide 18 by 6.
The value is 3.
M1 — Divide 18 by 6.
A1 — Answer 3
Question 3 Medium2 marks
2/5 of a number is 12. What is the number?
Show answer
Answer: 30
1/5 is 12 ÷ 2.
The whole is 5 of those parts.
M1 — 1/5 is 12 ÷ 2.
A1 — Answer 30
Question 4 Medium2 marks
48 tickets are for sale. 5/8 have been sold. How many are left?
Show answer
Answer: 18
3/8 are left.
48 × 3 ÷ 8.
M1 — 3/8 are left.
A1 — Answer 18
Question 5 Hard2 marks
Sam has 2/3 of 36 stickers and gives half of those away. How many does Sam keep?
Show answer
Answer: 12
2/3 of 36 comes first.
Then keep half of that.
M1 — 2/3 of 36 comes first.
A1 — Answer 12
Question 6 Hard2 marks
3/4 of a crowd is 18 people. How many people are in the other quarter?
Show answer
Answer: 6
3 parts are 18.
1 part is the other quarter.
M1 — 3 parts are 18.
A1 — Answer 6
Question 7 Exam-style3 marks
Sam has 2/3 of 54 stickers and gives half of those away. How many does Sam keep?
Show answer
Answer: 18
2/3 of 54 comes first.
Then keep half of that.
M1 — 2/3 of 54 comes first.
M1 — Then keep half of that.
A1 — Answer 18
Common mistakes
Most lost marks on this topic are one slip.
Multiplying by the denominator.
Divide by the denominator to find one part.
Stopping after one part when the numerator is more than 1.
Multiply the one part by the numerator.
Taking the fraction of the wrong total.
Read which amount the fraction applies to.
Giving the part that was used when the question asks for what is left.
Take the part used away from the total, then write the amount left.
Leaving the unit off the answer.
Write the unit with the number, for example 560 g.
Spot the slip
What is 1/4 of 20?
5
4
16
Show the slip
5 Twenty split into 4 equal parts is 5.
Exam tips
This topic can appear on a calculator or a non-calculator paper. Show enough working for a method mark.
If the question says “show that”, the result is given. The marks are for the steps that reach it.
The method is the same on AQA-style and Edexcel-style papers.
Write the division and the multiplication on separate lines: each is a method mark.
If the total does not divide exactly by the denominator, check you have read the question correctly — GCSE numbers are usually chosen to work.
Printable worksheet
The same questions are in a PDF you can print. Answers start on a later page.