A proportion is an equation stating that two ratios are equal. Proportions are used to solve problems involving scaling, similarity, maps, recipes, and any situation where quantities change at the same rate.

Cross-multiplication is the most common method for solving proportions. If a/b = c/d, then a × d = b × c. This technique transforms a proportion into a simple equation that can be solved with basic algebra.

Scale drawings and maps use proportions constantly. If 1 inch on a map represents 50 miles, a distance of 3 inches represents 150 miles. Understanding this proportional relationship helps students work with blueprints, models, and maps.

Proportional reasoning extends to similar figures in geometry, percent problems, and rate calculations. Students who master proportions develop flexible thinking about multiplicative relationships that serves them well in algebra, science, and everyday problem-solving.