Ratio & Proportion

Ratios compare quantities, rates compare quantities with different units, and proportion says two ratios are equal. These articles show how to share in a ratio, find the better deal with a unit rate, and solve a proportion by cross-multiplying.

Ratios Explained: Simplifying and Sharing in a Ratio
A ratio compares the sizes of two or more quantities. $2 : 3$ means that for every $2$ of the first there are $3$ of the second.
Rates and Unit Rates: Speed, Best Buys and Per-One Comparisons
A rate compares two quantities measured in different units, such as $150$ km in $3$ hours. A unit rate scales it to one of the second quantity: $50$ km per hour.
Direct Proportion and Cross-Multiplication
A proportion says two ratios are equal, such as $\frac{3}{7.50} = \frac{5}{x}$ . Two quantities are directly proportional when one is always the same multiple of the other: $y = kx$ .