Subtract fractions - Same denominator
Theory
To subtract fractions with the same denominator, subtract the numerators and keep the denominator. Then write the answer in its simplest form if the top and bottom share a factor.
When the denominators match, the parts are the same size.
Subtract the numerators and write the difference over the same denominator: \(\dfrac{4}{5}-\dfrac{1}{5}=\dfrac{3}{5}\).
Then write the answer in its simplest form if the top and bottom share a common factor.
Subtract the numerators over the shared denominator, then simplify if you can.
| Difference | Subtract tops | Simplest form |
|---|---|---|
| \(\dfrac{4}{5}-\dfrac{1}{5}\) | \(\dfrac{3}{5}\) | \(\dfrac{3}{5}\) |
| \(\dfrac{3}{4}-\dfrac{1}{4}\) | \(\dfrac{2}{4}\) | \(\dfrac{1}{2}\) |
| \(\dfrac{5}{6}-\dfrac{1}{6}\) | \(\dfrac{4}{6}\) | \(\dfrac{2}{3}\) |
How to subtract fractions with the same denominator
- Subtract the numerators.
- Keep the denominator the same.
- Simplify the answer if the top and bottom share a factor.
Subtract the numerators, keep the denominator.
| \(\dfrac{4}{5}-\dfrac{1}{5}\) | \(=\) | \(\dfrac{3}{5}\) |
| \(\dfrac{3}{4}-\dfrac{1}{4}\) | \(=\) | \(\dfrac{2}{4}\) |
| \(=\) | \(\dfrac{1}{2}\) |
| \(\dfrac{5}{6}-\dfrac{1}{6}\) | \(=\) | \(\dfrac{4}{6}\) |
| \(=\) | \(\dfrac{2}{3}\) |
| \(\dfrac{7}{8}-\dfrac{3}{8}\) | \(=\) | \(\dfrac{4}{8}\) |
| \(=\) | \(\dfrac{1}{2}\) |
Common pitfalls
Frequently asked questions
How do you subtract fractions with the same denominator?
Subtract the numerators and keep the denominator. \(\dfrac{4}{5}-\dfrac{1}{5}=\dfrac{3}{5}\).
Do you subtract the denominators?
No. The denominator is the size of the parts and stays the same; only the numerators are subtracted.
Do you have to simplify the answer?
Yes, write it in simplest form when the top and bottom share a common factor, such as \(\dfrac{2}{4}=\dfrac{1}{2}\).
Which fraction goes first?
The larger fraction goes first, so you take the smaller from the larger and the answer is not negative.