Explain how to subtract related unit fractions | Maths

Starter quiz

$What fraction of the shape is shaded?$

What fraction of the shape is shaded?
- ${2} \over {9}$ ✓
- ${2} \over {7}$
- ${1} \over {4}$
- ${7} \over {9}$
$What fraction of the shape is shaded?$

What fraction of the shape is shaded?
- ${3} \over {9}$ ✓
- ${1} \over {6}$
- ${1} \over {9}$
- ${6} \over {9}$
Tick the fractions in their simplest form.
- ${5} \over {15}$
- ${11} \over {14}$ ✓
- ${1} \over {6}$ ✓
- ${2} \over {18}$
$What fraction of the whole shape is shaded?$

What fraction of the whole shape is shaded?
- ${4} \over {16}$
- ${4} \over {12}$ ✓
- ${1} \over {8}$
- ${1} \over {3}$ ✓
Tick the sum in its simplest form. ${3} \over {5}$ + ${7} \over {5}$ =
- ${10} \over {5}$
- $1 {5} \over {5}$
- 2 ✓
- ${10} \over {10}$
- 1
Tick the difference in its simplest form. ${20} \over {4}$ − ${5} \over {4}$
- ${15} \over {4}$
- $3 {{3} \over {4}}$ ✓
- ${3} \over {4}$
- ${3} \over {2}$

Exit quiz

When one fraction has a denominator that is a multiple of another fraction, the fractions are called:
- related fractions. ✓
- common denominators.
- improper fractions.
- mixed numbers.
$This image shows <Math> {1} \over {4}</Math> − <Math> {1} \over {12}</Math> = ____ Tick the equation which shows the equivalent related fraction.$

This image shows ${1} \over {4}$ − ${1} \over {12}$ = ____ Tick the equation which shows the equivalent related fraction.
- ${2} \over {12}$ − ${1} \over {12}$ = ____
- ${3} \over {12}$ − ${1} \over {12}$ = ____ ✓
- ${4} \over {12}$ − ${1} \over {12}$ = ____
- ${5} \over {12}$ − ${1} \over {12}$ = ____
$This image shows <Math> {1} \over {5}</Math> − <Math> {1} \over {10}</Math> = ____ Tick the equation which shows the appropriate related fraction.$

This image shows ${1} \over {5}$ − ${1} \over {10}$ = ____ Tick the equation which shows the appropriate related fraction.
- ${2} \over {10}$ − ${1} \over {10}$ = ____ ✓
- ${3} \over {15}$ − ${1} \over {10}$ = ____
- ${4} \over {20}$ − ${1} \over {10}$ = ____
- ${5} \over {25}$ − ${1} \over {10}$ = ____
$This image shows <Math> {1} \over {5}</Math> − <Math> {1} \over {20}</Math> = ____ Tick the equation which shows the appropriate related fraction.$

This image shows ${1} \over {5}$ − ${1} \over {20}$ = ____ Tick the equation which shows the appropriate related fraction.
- ${2} \over {10}$ − ${1} \over {20}$ = ___
- ${3} \over {15}$ − ${1} \over {20}$ = ___
- ${4} \over {20}$ − ${1} \over {20}$ = ___ ✓
- ${5} \over {25}$ − ${1} \over {20}$ = ___
Tick the correct equation once it has been adjusted to include the most appropriate related fraction. ${1} \over {4}$ − ${1} \over {12}$ = ___
- ${1} \over {4}$ − ${3} \over {4}$ = ___
- ${2} \over {8}$ − ${1} \over {12}$ = ___
- ${3} \over {12}$ − ${1} \over {12}$ = ___ ✓
- ${1} \over {8}$ − ${1} \over {8}$ = ___
Tick the correct solution: ${1} \over {8}$ − ${1} \over {16}$ = ___
- ${1} \over {8}$
- ${1} \over {4}$
- ${1} \over {16}$ ✓
- ${2} \over {16}$

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 subtract them.
Common multiples help you to convert a fraction to a common denominator.
The language of unitising helps you to subtract fractions with the same denominators.
When subtracting fractions with the same denominators you just subtract the numerators.

Common misconception

Pupils try to subtract the numerators and the denominators from one another for each fraction.

Represent each fraction using a model that draws out the equivalence of the fractions and the need for the same counting unit (denominator). Revisit previous analogies regarding sharing a common counting unit such as animals for cats and dogs.

Keywords

Related fractions - When the denominator of one fraction is a multiple of the denominator of another fraction, we can say these fractions are related fractions.
Common denominator - When two or more fractions share the same denominator, you can say they have a common denominator.