Simplify a ratio to its lowest terms, and scale it proportionally to a new value — useful for recipes or scale drawings.
A ratio A : B is simplified by dividing both numbers by their greatest common divisor (GCD):
To scale a ratio proportionally — that is, to find what B becomes if A changes to a new value C — use:
A common example is scaling a recipe: if a recipe for 4 people uses 6 dl of flour, and you're cooking for 10 people, the ratio is 4 : 6, and the amount of flour becomes 10 × (6 ÷ 4) = 15 dl. The same principle is used in map scales and drawings, where the ratio between distance on the map and actual distance stays constant.
A ratio shows the relationship between two quantities, written as A : B. It tells you how many times larger or smaller one value is compared to the other, without saying anything about the actual sizes.
Divide both numbers in the ratio by their greatest common divisor (GCD). For example, 4 : 6 simplifies to 2 : 3 by dividing both numbers by 2.
Set up the ratio between the two quantities (e.g. number of people and amount of ingredient), and scale proportionally: new amount = new value × (original amount ÷ original value). The same method is used for scale on maps and drawings.