Adding and subtracting fractions
Find a common denominator, then add or subtract the numerators. Year 5/6.
Same denominator: just add the numerators (⅕ + ⅖ = ⅗). Different denominators: find a common denominator (LCM of the two denominators) before adding. Year 6 mixes whole numbers and fractions.
Worked examples
¼ + ½ = ¼ + &frac24; = ¾.
⅔ + ⅕ = &frac{10}{15} + &frac{3}{15} = &frac{13}{15}.
2¾ - 1½ = 1¼. Convert: &frac{11}{4} - &frac{3}{2} = &frac{11}{4} - &frac{6}{4} = &frac{5}{4} = 1¼.
Frequently asked questions
Why find a common denominator?
You can only add fractions of the same kind. ¼ and ½ are different sizes; making them both quarters lets us add.
Always the LCM?
The LCM gives the smallest answer. Multiplying the two denominators always works but may need simplifying afterwards.