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 ±«Óătv Teach series, Hyaptia's Mathematical Maze.
±«Óătv Teach has thousands of free, curriculum-linked resources to help deliver lessons - all arranged by subject and age group.
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