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Proportion
See It in Action
Two examples of the idea done right—and one common look-alike that is not right.
EXAMPLE
EXAMPLE
NON-EXAMPLE
Definition
A proportion is an equation that shows two ratios are equal.
For example, 2/3 = 4/6
This is a proportion because both ratios represent the same amount.
Example
If a recipe uses 2 cups of flour for every 3 cups of sugar, then doubling the recipe gives:
2/3 = 4/6
The relationship stays the same, so the ratios form a proportion.
Key Idea
In a proportion, ab=cd, the cross products are equal: a•d=b•c
For example:
3/5 = 12/20
Since 3 x 20 = 60 and 5 x 12 = 60 the ratios are proportional.
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