Definition
Proportion
An equation showing that two ratios have the same value.
What it means
A proportion says that two comparisons are equivalent. You can scale both parts of one ratio by the same factor, and the comparison keeps the same value.
Remember it
Two ratio names, one value.
Example
A drink uses 2 scoops of powder for 5 cups of water. Using 8 scoops for 20 cups gives 2/5 = 8/20, so the equation is a proportion.
Watch for
Here, proportion means an equality of ratios. It does not mean only a share or part of a whole.
Common mix-up
Two ratios do not form a proportion just because every number became larger; both ratios must have the same value.
Exact meaning
A proportion is an equation stating that two ratios are equal, such as a/b = c/d, with nonzero denominators.