Explain with and without images how to add and subtract related non-unit fractions bridging a whole | Maths

Starter quiz

Tick the non-unit fractions.
- ${3} \over {6}$ ✓
- ${9} \over {4}$ ✓
- ${1} \over {7}$
- ${2} \over {1}$ ✓
12 inches is equivalent to one __________.
- metre
- yard
- foot ✓
- kilogram
Tick the pairs of related fractions.
- ${1} \over {5}$ ${2} \over {9}$
- ${1} \over {4}$ ${7} \over {12}$ ✓
- ${3} \over {6}$ ${4} \over {24}$ ✓
- ${1} \over {5}$ ${1} \over {25}$ ✓
Select the fraction which is ${6} \over {9}$ in its simplest form.
- ${1} \over {6}$
- ${1} \over {3}$
- ${2} \over {3}$ ✓
- ${1} \over {9}$
${1} \over {5}$ + ${3} \over {15}$ = ___
- ${3} \over {20}$
- ${1} \over {20}$
- ${3} \over {15}$
- ${6} \over {15}$ ✓
- ${2} \over {5}$ ✓
Match each fraction to a related fraction.
- ${1} \over {4}$
  
  ⇔
  
  ${5} \over {16}$ ✓
- ${1} \over {9}$
  
  ⇔
  
  ${8} \over {36}$ ✓
- ${1} \over {5}$
  
  ⇔
  
  ${6} \over {35}$ ✓
- ${1} \over {6}$
  
  ⇔
  
  ${32} \over {66}$ ✓

Exit quiz

One foot is equivalent to ______ inches.
- '12' ✓
What is the value of the numerator in this diagram?
- '9' ✓
What is the value of the missing numerator?
- '2' ✓
Tick the expressions that represent the shaded parts of these bars being added together.
- ${3} \over {4}$ + ${3} \over {12}$
- ${3} \over {12}$ + ${4} \over {3}$
- ${3} \over {4}$ + ${4} \over {12}$ ✓
- ${9} \over {12}$ + ${4} \over {12}$ ✓
$1{{4} \over {12}}$ − ${10} \over {24}$ =
- ${20} \over {22}$
- ${22} \over {24}$ ✓
- ${2} \over {12}$
- ${11} \over {12}$ ✓
- ${12} \over {24}$
$1 {{3} \over {6}}$ − ${8} \over {12}$ + ${4} \over {24}$ =
- ${1} \over {24}$
- ${12} \over {12}$ ✓
- ${24} \over {12}$
- ${24} \over {24}$ ✓
- ${6} \over {6}$ ✓

Worksheet

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Presentation

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Lesson Details

Key learning points

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.
When the sum of the numerators is greater than the denominator you can convert the improper fraction to a mixed number.

Common misconception

Pupils think that the largest denominator of the related fraction should only be used as the common denominator.

Provide examples where fractions can be scaled up or scaled down to find an appropriate common denominator and encourage pupils to discuss which strategy they prefer and why.

Keywords

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