By Zencalcy Editorial TeamLast reviewed About us
Two tools in one: reduce a ratio like 12:18 to 2:3 using the greatest common divisor, or solve a proportion A : B = C : D by leaving exactly one value blank.
Simplify ratios with GCD or solve A:B = C:D proportions.
Simplified = a/g : b/g (g = GCD); proportion: A/B = C/D
| Symbol | Meaning |
|---|---|
| a : b | Ratio to simplify (whole numbers) |
| A : B = C : D | Proportion with one unknown |
12:18 simplifies to 2:3 (÷6). Proportion 2:3 = 4:D gives D = 6.
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Both parts are divided by their greatest common divisor — the largest number dividing both — e.g. GCD(12,18) = 6.
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Content updated: September 2026