Add & Subtract Fractions
See the common-denominator method step by step, with the final answer fully simplified.
- 1
The problem.
1/2 + 1/3
- 2
Find the common denominator: the LCM of 2 and 3 is 6.
1/2 = 3/6 (×3)
1/3 = 2/6 (×2)
- 3
Now add the numerators (keep the denominator).
3/6 + 2/6 = 5/6
5/6
About the Add & Subtract Fractions
Adding fractions with different denominators is really three skills stacked on top of each other: finding a common denominator, converting both fractions to match it, and only then combining the numerators. Most fraction mistakes happen because a student skips straight to adding the numerators they started with. This tool keeps those three moves visually separate so the order can't get lost.
I assign this for independent practice after I've taught common denominators directly, since it won't do the conceptual teaching for you — it shows the conversion math plainly enough that a student who's a little shaky can follow along and self-correct.
How to use it in your classroom
- Enter a numerator and denominator for the first fraction, choose addition or subtraction, then enter the second fraction.
- Read the problem statement in the first step card to confirm the operation was entered correctly.
- If the denominators differ, review the common-denominator step, which shows exactly what each fraction was multiplied by to match the new denominator.
- Check the combine step, which adds or subtracts the converted numerators over the shared denominator.
- If the result can be simplified, review the simplify step showing the greatest common factor used to reduce it.
- Read the final answer, which converts to a mixed number automatically when the result is greater than one.
Tips from the classroom
- Start with two fractions that already share a denominator so students see the combine-and-simplify steps without the common-denominator step adding noise.
- Use denominators that aren't multiples of each other, like 4 and 6, so the least common denominator step actually has work to show instead of just matching the larger number.
- Build in a problem where the answer simplifies to a whole number and ask students to predict that outcome before checking the simplify step.
- Switch to subtraction with the second fraction larger than the first and let students notice the negative numerator the tool produces — it's a useful prompt for a discussion about negative fractions.
Frequently asked questions
Does the tool show how it finds the common denominator?
Yes. It uses the least common multiple of the two denominators and shows exactly what each fraction is multiplied by to reach that shared denominator before combining.
What happens if the answer can be simplified further?
A separate step appears showing the greatest common factor of the numerator and denominator and the reduced fraction that results from dividing both by it.
Will the tool convert an improper fraction to a mixed number?
Yes, whenever the final numerator's absolute value exceeds the denominator, the answer line shows both the improper fraction and its mixed-number equivalent.