What Is a Ratio?
Definition
Ratio: A comparison of two quantities by division. The ratio of a to b is written a / b or a : b, and b cannot be zero; if 3 pens cost 12, the ratio of price to pens is 4.
A ratio compares two quantities by division. The ratio of a to b is written a / b or a : b, and b cannot be zero. Unit prices and speeds are ratios. For example, if 3 pens cost 12, the ratio of price to pens is 12 / 3 = 4, or 4 per pen.
Where it appears in the formulas
In the proportion calculator, the constant of proportionality is a ratio. In a direct proportion k = b / a: if 3 pens cost 12, k = 12 / 3 = 4. The percentage change calculator also gives the ratio of the new value to the old one: ratio = new / old. Going from 250 to 300, the ratio is 1.2.
Ratio and proportion
A ratio is a single division. A proportion is an equation of two ratios: a / b = c / x. When you know both terms of one ratio, a proportion gives the value that goes with a new one.