Proportion

Last updated 2026-06-19

Definition

A proportion is a mathematical statement that two ratios are equal: $\frac{a}{b} = \frac{c}{d}$ .

Why It Matters

Proportions are the equations of scale, letting us solve for unknown parts of similar figures, chemical mixtures, and rates of change.

Core Concepts

Proportion Equation: $\frac{a}{b} = \frac{c}{d}$ $\frac{a}{b} = \frac{c}{d}$
- How to read: “a over b equals c over d.”
- Meaning: The relation between the values is constant.
Cross-Multiplication: If $\frac{a}{b} = \frac{c}{d}$ $\frac{a}{b} = \frac{c}{d}$ , then $ad = bc$ $a d = b c$ .
- How to read: “a times d equals b times c.”
- Meaning / when to use: Simplifies proportion equations to solve for a single unknown.

Connected Concepts

Connected notes