Simplifying Fractions
Use common factors to simplify fractions to their simplest form; use common multiples to express fractions with a common denominator
What a learner can do afterwards
- Simplify 18/24 to 3/4 by identifying the HCF of 18 and 24
- Express 2/3 and 5/8 with a common denominator of 24
- Explain why dividing numerator and denominator by a common factor produces an equivalent fraction
The lesson
A fraction can look different but still stand for the same amount. Simplifying a fraction means writing it with the smallest possible numbers, without changing what it means. You do this by dividing the numerator and denominator by their highest common factor, or HCF.
To simplify 18/24, find the HCF of 18 and 24. It is 6. Divide both numbers by 6: 18 divided by 6 is 3, and 24 divided by 6 is 4. So 18/24 simplifies to 3/4.
Sometimes you need two fractions to share the same denominator instead, so you can compare or add them. Find a common multiple of both denominators. For 2/3 and 5/8, a common denominator is 24, because 24 is a multiple of both 3 and 8.
To simplify fast, look for the biggest number that divides evenly into both the top and bottom. To find a common denominator, multiplying the two denominators together always works, even when it is not the smallest option.
Divide by the HCF to simplify a fraction, and use a common multiple of the denominators to give two fractions a matching bottom number.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.