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What is a ratio?

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Quick answer

A ratio is a way of comparing two or more quantities, showing how much of one there is relative to another. Written with a colon — like 2:3 — it means 'for every 2 of the first thing, there are 3 of the second'. Recipes, maps, and mixtures all use ratios.

Key things to understand

  1. A ratio compares quantities: 2:3 means 2 parts of one to 3 parts of another.
  2. Ratios can be scaled up or down while staying equivalent — 2:3 = 4:6 = 10:15.
  3. Order matters: 2:3 is different from 3:2.
  4. A ratio can be written as a fraction and relates closely to proportions.
  5. Used in cooking (mix 1:2), maps (scale 1:1000), and finance (debt-to-income ratio).

People also ask

How do you read a ratio?
A ratio like 2:3 is read 'two to three' — for every 2 of the first quantity there are 3 of the second. It compares their relative sizes.
What's the difference between a ratio and a fraction?
A fraction compares a part to the whole (¾ = 3 of 4 total parts); a ratio compares parts to each other (3:1 = 3 of one to 1 of another). They're related but answer different questions.
Can ratios be simplified?
Yes, like fractions — divide both sides by the same number. 10:15 simplifies to 2:3 by dividing both by 5.