Which statement about rates is true?

• A. A ratio using the same units.
• B. A ratio of quantities using different units.
• C. A sum of quantities.
• D. The product of quantities.

Answer: (B)

Rates are a way to compare two quantities that have different units, showing how much of one thing happens for a certain amount of another. That’s why a rate is best described as a ratio of quantities using different units. Think of speeding as miles per hour, or the cost you pay per item, or fuel efficiency as liters per 100 kilometers—the units in the numerator and denominator are different, and the rate tells you how much of the first quantity corresponds to one unit (or some fixed amount) of the second.

This isn’t about adding quantities together (that would be a sum) or multiplying them (that would be a product). It’s about division to compare two different kinds of quantities. So the statement that a rate is a ratio of quantities using different units captures the true idea.