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Year 3

Add fractions with the same denominator and generalise the rule

I can add fractions with the same denominator and generalise the rule.

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Share activities with pupils
New
New
Year 3

Add fractions with the same denominator and generalise the rule

I can add fractions with the same denominator and generalise the rule.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. To add fractions with the same denominator you add the numerators using the language of unitising.
  2. If 2 plus 3 is equal to 5 then 2 one sevenths plus 3 one sevenths is equal to 5 one sevenths.
  3. If fractions have the same denominator they can be added.

Common misconception

In the addition of fractions, many children will try to add together both the numerator and denominator.

Show the children many completed examples using representations alongside the fraction notation. Encourage them to make generalisations and spot that the denominator remains the same because it is the unit.

Keywords

  • Generalisation - A generalisation is a statement or rule that applies correctly to all relevant cases.

  • Denominator - A denominator is the bottom number in a fraction. It shows how many parts a whole has been divided into.

  • Numerator - A numerator is the top number in a fraction. It shows how many parts we have.

Encourage discussion here. Generalisation shouldn't just be waiting until the teacher gives the answer. Use your learning wall if available to record thoughts, observations and then the final generalisation.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Video

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Starter quiz

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6 Questions

Q1.
Which of these definitions describes the sum?
A number added to another number.
Correct answer: All of the parts added together.
Q2.
What is the missing number in this bar model?
An image in a quiz
Correct Answer: 2, two
Q3.
What addition is being shown by this number line?
An image in a quiz
10 = 50 + 40
40 + 10 = 50
Correct answer: 10 + 40 = 50
40 = 50 + 10
Q4.
Each marble in a bag is $$ \frac{1}{9} $$ of the whole bag. How many marbles are there in the bag?
1
10
Correct answer: 9
12
Q5.
What is the missing fraction in this bar model?
An image in a quiz
$$ \frac{1}{3} $$
$$ \frac{1}{4} $$
Correct answer: $$ \frac{1}{5} $$
$$ \frac{1}{6} $$
Q6.
Select the correct sum. $$ \frac{2}{7} $$ + $$ \frac{4}{7} $$ = ___
Correct answer: $$ \frac{6}{7} $$
$$ \frac{7}{6} $$
$$ \frac{6}{14} $$
$$ \frac{8}{14} $$

Exit quiz

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6 Questions

Q1.
Look at the image. What is the missing label marked with a question mark?
An image in a quiz
addend
Correct answer: sum
part
Q2.
Look at the number line. The missing addend is ___
An image in a quiz
$$ \frac{1}{10} $$
Correct answer: $$ \frac{2}{10} $$
$$ \frac{3}{10} $$
$$ \frac{5}{10} $$
Q3.
What addition is being represented on this number line?
An image in a quiz
$$ \frac{1}{8} $$ + $$ \frac{4}{8} $$ = $$ \frac{3}{8} $$
$$ \frac{6}{8} $$ + $$ \frac{5}{8} $$ = $$ \frac{1}{8} $$
$$ \frac{3}{8} $$ + $$ \frac{3}{8} $$ = $$ \frac{6}{8} $$
Correct answer: $$ \frac{1}{8} $$ + $$ \frac{3}{8} $$ = $$ \frac{4}{8} $$
Q4.
What is the sum of this equation? $$ \frac{3}{7} $$ + $$ \frac{2}{7} $$ + $$ \frac{1}{7} $$ = ___
$$ \frac{6}{14} $$
$$ \frac{8}{7} $$
Correct answer: $$ \frac{6}{7} $$
Q5.
What is the correct sum for this equation? ___ = $$ \frac{4}{20} $$ + $$ \frac{6}{20} $$+ $$ \frac{6}{20} $$
Correct answer: $$ \frac{16}{20} $$
$$ \frac{10}{20} $$
$$ \frac{15}{60} $$
Q6.
Which of the following numbers could be used to complete this inequality?
An image in a quiz
Correct answer: 1
Correct answer: 2
3
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