GUIDE深度 · Deep dive
Adding and Subtracting Fractions
If denominators differ, find the least common multiple, convert both fractions, add/subtract the numerators, then reduce. Improper fractions are fine.
Steps
Find the LCM of denominators.
Scale numerators by the same factor.
Add/subtract numerators; keep denominator.
Reduce.
Example
1/2 + 1/3 = 3/6 + 2/6 = 5/6.
3/4 - 1/6 = 9/12 - 2/12 = 7/12.
FAQ
Why not add denominators?
Denominators are unit sizes; different units cannot be added directly.
Must I use the LCM?
Not required, but the LCM keeps numbers smaller.