Explain with and without an image how to add and subtract related non-unit fractions | Maths

Starter quiz

Tick the non-unit fractions.
- ${1} \over {3}$
- ${4} \over {7}$ ✓
- ${5} \over {4}$ ✓
- ${1} \over {8}$
Tick the largest fraction.
- ${1} \over {4}$
- ${2} \over {7}$
- ${3} \over {6}$
- ${8} \over {9}$ ✓
Tick the pairs of related fractions.
- ${1} \over {3}$ ${2} \over {6}$ ✓
- ${1} \over {4}$ ${3} \over {16}$ ✓
- ${2} \over {7}$ ${4} \over {21}$ ✓
- ${1} \over {5}$ ${1} \over {12}$
Tick the expression that matches this image.
- ${4} \over {6}$ + ${1} \over {12}$
- ${3} \over {6}$ + ${1} \over {12}$
- ${1} \over {6}$ + ${1} \over {12}$ ✓
- ${1} \over {6}$ + ${5} \over {12}$
Select the fraction which is ${8} \over {12}$ in its simplest form.
- ${4} \over {6}$
- ${2} \over {3}$ ✓
- ${1} \over {12}$
- ${1} \over {8}$
Match each fraction to a related fraction.
- ${1} \over {3}$
  
  ⇔
  
  ${7} \over {21}$ ✓
- ${1} \over {4}$
  
  ⇔
  
  ${8} \over {36}$ ✓
- ${1} \over {5}$
  
  ⇔
  
  ${9} \over {55}$ ✓
- ${1} \over {6}$
  
  ⇔
  
  ${24} \over {72}$ ✓

Exit quiz

Tick the non-unit fractions.
- ${1} \over {9}$
- ${2} \over {7}$ ✓
- ${3} \over {8}$ ✓
- ${1} \over {10}$
- ${8} \over {3}$ ✓
Tick the related non-unit fraction for ${1} \over {4}$
- ${1} \over {8}$
- ${1} \over {12}$
- ${3} \over {16}$ ✓
- ${12} \over {3}$
Tick the pairs of related fractions.
- ${1} \over {4}$ ${3} \over {12}$ ✓
- ${4} \over {6}$ ${2} \over {12}$ ✓
- ${8} \over {15}$ ${3} \over {5}$ ✓
- ${1} \over {6}$ ${2} \over {4}$
Tick the expression that matches this image.
- ${1} \over {3}$ + ${3} \over {15}$ ✓
- ${2} \over {3}$ + ${1} \over {15}$
- ${3} \over {3}$ + ${5} \over {15}$
- ${1} \over {3}$ + ${3} \over {10}$
${8} \over {9}$ − ${2} \over {18}$ = ___
- ${14} \over {18}$ ✓
- ${7} \over {9}$ ✓
- ${2} \over {9}$
- ${7} \over {18}$
- ${14} \over {9}$
${3} \over {7}$ + ${3} \over {21}$ = ___
- ${14} \over {21}$
- ${4} \over {21}$
- ${12} \over {21}$ ✓
- ${14} \over {42}$
- ${6} \over {28}$

Worksheet

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Presentation

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Lesson Details

Key learning points

You can use knowledge of common multiples to convert fractions to an equivalent with a common denominator.
In equivalent fractions, the numerators and denominators have been scaled up or down by the same factor.
Fractions need to have the same denominator if you are to add and subtract them.
When adding or subtracting fractions with the same denominators you just add or subtract the numerators,

Common misconception

Pupils add or subtract the numerators and denominators from eachother to find the solution.

Ensure pupils don't move to abstract equations straight away until they are secure with how addition and subtraction of non-unit fractions can be represented pictorially. You can use unitised language: ___ fifths plus ___ fifths = ___ fifths.

Keywords

Common denominator - When two or more fractions share the same denominator, you can say they have a common denominator.