Key Concepts

• Proportion
  • A proportion is an equation of the form ${\Large\frac{a}{b}}={\Large\frac{c}{d}}$, where $b\ne 0$, $d\ne 0$.  The proportion states two ratios or rates are equal. The proportion is read “$a$ is to $b$, as $c$ is to $d$“.
• Cross Products of a Proportion
  • For any proportion of the form ${\Large\frac{a}{b}}={\Large\frac{c}{d}}$ , where $b\ne 0$ , its cross products are equal: $a\cdot d=b\cdot c$ .
• Percent Proportion
  • The amount is to the base as the percent is to 100. ${\Large\frac{\text{amount}}{\text{base}}}={\Large\frac{\text{percent}}{100}}$

Glossary

proportion

A proportion is an equation of the form ${\Large\frac{a}{b}}={\Large\frac{c}{d}}$ , where $b\ne 0$ , $d\ne 0$ .The proportion states two ratios or rates are equal. The proportion is read ” $a$ is to $b$ , as $c$ is to $d$ “.