Fraction operations
Add and subtract fractions with unlike denominators; multiply and divide fractions; perform multi-step calculations with mixed numerals.
Worked examples
Adding fractions with unlike denominators
Straightforward
Problem
Calculate .
1
Find the lowest common denominator (LCD) of 3 and 8.
The multiples of 3 are 3, 6, 9, 12, 15, 18, 21, 24, … and the multiples of 8 are 8, 16, 24, … The LCD is 24.
2
Convert each fraction to an equivalent fraction with denominator 24.
3
Add the numerators, keeping the denominator the same.
Answer
Dividing fractions and simplifying
Moderate
Problem
Calculate . Give your answer in simplest form.
1
Change the division to multiplication by taking the reciprocal of the second fraction.
2
Multiply numerators together and denominators together.
3
Simplify by dividing the numerator and denominator by their highest common factor (HCF = 6).
Answer
Adding mixed numerals in a word problem
Challenging
Problem
A painter uses litres of paint on Monday and litres on Tuesday. How many litres did the painter use in total?
1
Convert each mixed numeral to an improper fraction.
2
Find the LCD of 4 and 3, then rewrite each fraction with that denominator.
3
Add the fractions.
Answer
litres
Practise
Q1·Straightforward
Calculate . Give your answer as a fraction in simplest form.
/
Explanation
The LCD of 3 and 4 is 12. Converting: and . Adding: .
Q2·Straightforward
Calculate . Give your answer as a fraction in simplest form.
/
Explanation
The LCD of 4 and 3 is 12. Converting: and . Subtracting: .
Q3·Straightforward
Calculate . Give your answer as a fraction in simplest form.
/
Explanation
The LCD of 5 and 4 is 20. Converting: and . Adding: .
Q4·Straightforward
Calculate . Give your answer as a fraction in simplest form.
/
Explanation
The LCD of 6 and 4 is 12. Converting: and . Subtracting: .
Q5·Moderate
Calculate . Give your answer in simplest form.
/
Explanation
.
Q6·Moderate
Calculate . Give your answer as a fraction in simplest form.
/
Explanation
.
Q7·Moderate
Calculate . Give your answer in simplest form.
/
Explanation
.
Q8·Moderate
Calculate . Give your answer as a fraction in simplest form.
/
Explanation
.
Q9·Challenging
Calculate . Give your answer as an improper fraction in simplest form.
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Explanation
and . The LCD of 2 and 3 is 6. Converting: and . Adding: .
Q10·Challenging
Calculate . Give your answer as an improper fraction in simplest form.
/
Explanation
and . Multiplying: .
Q11·Challenging
A bag of rice weighs kg. A shop orders bags. What is the total weight in kilograms? Give your answer as a fraction.
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Explanation
and . Total weight kg.
Q12·Challenging
Calculate . Give your answer as a fraction in simplest form.
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Explanation
and . Writing all terms with denominator 4: .