Common Factors (GCF, LCM, LCD)
Prime factorization, greatest common factor, least common multiple, and lowest common denominator.
This page is a free outline of what the Common Factors (GCF, LCM, LCD) lesson covers — it is not the lesson itself. The interactive lesson, practice, quizzes, and AI Tutor are inside the app.
This lesson covers
- Factors and Multiples A factor divides evenly into a number (3 is a factor of 12); a multiple is a number you reach by counting up by it (12, 24, 36 are multiples of 12).
- Fractions – Simplifying To simplify a fraction, divide its numerator and denominator by their greatest common factor, reducing it to lowest terms.
- GCF (Greatest Common Factor) The GCF is the largest number that divides evenly into two numbers — your tool for simplifying, like reducing a fraction. Find it by listing factors, or by multiplying the primes both numbers share.
- LCD (Lowest Common Denominator) The LCD is the least common multiple of two denominators — the smallest bottom number both fractions can share so you can add or subtract them.
- LCM (Lowest Common Multiple) The LCM is the smallest number that both numbers divide into — your tool for combining fractions with different denominators. Find it by listing multiples, or by taking the highest power of every prime in either number.
- Prime Factorization
Linked concepts (purple →) have a full explanation. Hover or tap a dotted ⓘ concept for a quick definition.
Inside the app, Common Factors (GCF, LCM, LCD) comes with:
Read the explanation here for free — then practice it for real, with everything you need in one place.
24/7 AI Tutor — Ask anything and get a step-by-step explanation when you’re stuck — it teaches the concept, not just the answer. Every answer verified by three independent AIs.
- 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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