# Rate

A rate is a special kind of ratio, of two measurements with different units. It is a comparison of two measurements with different units, such as miles to gallons or cents to pounds. For example, suppose you spend 9 dollars on 2 pounds of candy. The rate \$9 / 2 pounds compares the money spent to the number of pounds of candy.

The division operator when dealing with units is sometimes expressed as "per". Also, if the units are expressed without abbreviation, the top unit is usually plural while the bottom is singular. For example, 5 meters / 3 seconds may be written as 5/3 meters/second.

Often rate is a synonimous of rhythm or frequency, such as heart rate or sample rate.

A unit rate is a rate that is simplified so it has a denominator of 1. This type of rate is frequently used when referring to statistics.

## Example

The civics membership in the U.S. House of Representatives is based on a population in the preceding census. In 1990, the population of the United States was about 248,000,000. There are 435 members in the house. On average, how many people are represented by each member of the house?

Write the rate that compares the population to the number of members of the house. Then divide both the numerator and the denominator by 435.

(248,000,000 people)/(435 members) ~ (570,000 people)/(1 member)

This is saying the each representative represents about 570,000 people.

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