Ratios & Proportional Relationships

What you’ll learn

• A ratio compares two quantities; equivalent ratios show the same relationship at different scales
• A unit rate expresses a rate "per one", useful for comparing prices, speeds, and densities
• A proportional relationship has a constant ratio $\frac{y}{x}$; its graph is a line through the origin with slope $k$
• The equation $y = kx$ models proportionality; $k$ is the constant of proportionality
• Percents are ratios out of $100$; scale drawings use a constant scale factor on every length