A worked example
The ratio 12:18 simplifies to 2:3. And if 2:3 = 10:x, then x = 15.
Frequently asked questions
How is a ratio different from a fraction?
They use the same math, but a ratio compares two separate quantities (3 cats to 5 dogs), while a fraction usually represents a part of one whole (3/5 of a pizza) — the relationship being expressed is conceptually different even though the simplification process is identical.
What's a real-world use for solving a proportion?
Scaling a recipe, converting a map distance to real distance, or figuring out how much of an ingredient you need if a ratio changes — anywhere two quantities need to stay in the same relative proportion as one of them changes.