Ratios, Proportions, and Percents

A ratio represents a relationship between quantities, not the actual quantities themselves. Fractions are an especially effective way to represent and work with ratios.

Pay close attention to units, and convert units if required by the question. Writing out the unit conversion as a series of multiplication steps, as seen here, will help ensure accuracy. Intermediate units should cancel, leaving you with the desired unit.

Percent is a type of proportion that means “per 100”; 20%, for instance, means 20 out of (or per) 100. Percent increase or decrease is calculated by finding the difference between two quantities, then dividing the difference by the original quantity and multiplying the result by 100.