Fractions – Adding and Subtracting
To add or subtract fractions, the denominators have to match — then you combine only the numerators.
This is a free explanation of Fractions – Adding and Subtracting — a preview, not the full interactive lesson. The lesson, practice, quizzes, and AI Tutor are inside the app.
To add or subtract fractions, the denominators have to match. If they already do (like fractions), just add or subtract the numerators and leave the denominator alone.
If the denominators don’t match (unlike fractions), find the lowest common denominator (LCD) first, convert each fraction to that denominator, then add or subtract the numerators. The bottom number is only a label for the size of the pieces — it never gets added.
A common mistake is adding the denominators: 1/3 + 1/4 is not 2/7. You only combine the numerators; the denominator stays the same or becomes the LCD.
Worked example
Add: 1/3 + 1/4
- The denominators are different, so find the LCD of 3 and 4 — the smallest number both divide into evenly, which is 12.
- Convert 1/3: multiply top and bottom by 4 → 4/12. Convert 1/4: multiply top and bottom by 3 → 3/12.
- Now they match: 4/12 + 3/12 = 7/12.
- Check: 7 is prime and does not divide 12, so 7/12 is already in simplest form.
7/12
On the test: The GED & HiSET give fractions in mixed and unlike forms; getting to a common denominator first is the key move.
Inside the app, Fractions – Adding and Subtracting comes with:
Read the explanation here for free — then practice it for real, with everything you need in one place.
- Practice sets — Open-book practice questions at your level, easiest-first — as many as you want, never scored.
- Quizzes — Scored quizzes on the whole lesson, so you know when you’re ready to move on.
- Skills Check — A concept-by-concept map of what you’ve mastered and what to focus on next.
- Worked examples — Tap the Brain Button on any example for alternative step-by-step explanations.
- Glossary — Plain-English definitions of every key term in the lesson.
- Formula sheet — The GED® & HiSET® formula sheets, on screen while you practice.
- Practice calculator — An on-screen calculator to build your calculator skills before test day.
- Math-fact flashcards — Quick drills for addition, multiplication, perfect squares, and square roots.
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