How it’s calculated
A proportion says two ratios are equal. Cross-multiplying turns it into an equation you can solve for any one missing term. To simplify a ratio, divide both terms by their greatest common divisor (decimals are first scaled to whole numbers).
Example: 3 : 4 = 6 : D gives D = 4 × 6 ÷ 3 = 8. Simplifying 12 : 16: the greatest common divisor is 4, so 12 : 16 = 3 : 4. A ratio of 1.5 : 2.5 is scaled to 15 : 25, which simplifies to 3 : 5.
Frequently asked questions
How do I scale a recipe with a ratio?
If a recipe for 4 uses 300 g of flour, for 6 people solve 4 : 300 = 6 : D. D = 300 × 6 ÷ 4 = 450 g.
What does 1 : n mean?
It rescales the ratio so the first term is 1. For 4 : 10 that is 1 : 2.5.
Is a ratio the same as a fraction?
A ratio A : B can be written as the fraction A/B, but ratios can also compare more than two quantities and are read as "A to B".
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Sources
- Prealgebra 2e, §5.6 Ratios and Rate — OpenStax
- Prealgebra 2e, §6.5 Solve Proportions and their Applications — OpenStax
Formulas are taken from the free public references above. Results are provided “as is” for informational and educational purposes only. See our disclaimer.
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