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About this video
How to add and subtract fractions with different denominators by finding a common denominator first. A core skill that shows up everywhere, from algebra to financial maths.
What it covers
- Why you need the same denominator before adding or subtracting
- Finding the lowest common denominator (LCD)
- Adding and subtracting mixed numbers
- Simplifying the answer
Extra worked examples
✍️ Extra example: ⅔ + ¼
- 1Find the LCD of 3 and 4, which is 12.12 is the smallest number both 3 and 4 divide into.
- 2Rewrite each fraction over 12: ⅔ = 8⁄12 and ¼ = 3⁄12.Multiply top and bottom by the same value.
- 3Add the numerators: 8⁄12 + 3⁄12 = 11⁄12.Once denominators match, add the tops only.
Exercises to try
Work each one out, then click to reveal the answer.
- 1½ + ⅓
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3⁄6 + 2⁄6 = 5⁄6 - 2¾ − ⅖
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15⁄20 − 8⁄20 = 7⁄20 - 31⅕ + ⅗
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6⁄5 + 3⁄5 = 9⁄5 = 1⅘
Practise this topic
Download matching Grade 8–9 papers and worksheets.
