Watch: Adding and subtracting fractions
Common denominators
It's easy to add and subtract fractions when the numbers on the bottom are the same.
These are called the denominators.
\( \frac{2}{9} \) + \( \frac{5}{9} \) = \( \frac{7}{9} \)
Equivalent fractions
However, sometimes the denominators are different.
\( \frac{1}{2} \) + \( \frac{1}{3} \) = ?
You can use equivalent fractions to make them the same.
A common multiple of 2 and 3 is 6.
So, for each fraction we need an equivalent fraction with a denominator of 6.
To find the equivalent fraction for \( \frac{1}{2} \) we need to multiply the numerator and denominator by 3.
\( \frac{1}{2} \) = \( \frac{3}{6} \)
And to find the equivalent fraction for\( \frac{1}{3} \) we must multiply the numerator and denominator by 2.
\( \frac{1}{3} \) = \( \frac{2}{6} \)
Now the denominators are the same we can add them together.
\( \frac{3}{6} \) + \( \frac{2}{6} \) = \( \frac{5}{6} \)
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Teaching resources
Looking for more teaching resources? This short animated film on adding and subtracting fractions is from the 大象传媒 Teach series, Hyaptia's Mathematical Maze.
大象传媒 Teach has thousands of free, curriculum-linked resources to help deliver lessons - all arranged by subject and age group.
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