Formula and method
A ratio a:b compares two quantities. Divide positive integer terms by their greatest common factor to simplify. Multiply both terms by the same factor to scale. A proportion a:b = c:d is solved by cross multiplication, ad = bc.
Worked example
12:18 simplifies to 2:3 after dividing by 6. Scaling 2:3 by 4 gives 8:12. In 12:18 = 8:d, d = 18 × 8 / 12 = 12.
Inputs and limitations
The percentage shown is a/b × 100, not a/(a+b) × 100. A 2:3 mixture contains 40% of the first ingredient, even though the ratio a/b is 66.6667%. Simplification accepts positive integers up to 10¹²; the other modes accept positive decimals.