Reading and Writing Percents

Definition of Percent

Interpret each of the following statements.

A mortgage interest rate is 6.3%.

A CD earns 2.85%.

Many people tip 15%.

Each of the problems involves percentages, which are a very common method for stating ratios involving monetary values. The mortgage interest rate means that a person must pay $6.30 for every $100 borrowed, which is a ratio of 6.3 to 100. The CD earns $2.85 for every $100 put into the CD, which is a ratio of 2.85 to 100. A tip of 15% means that the people tip $15 for every $100 paid for a meal, which is a ratio of 15 to 100 or 3 to 20.

Remember, in our last lesson, we stated that a ratio is a comparison of the relative size of two numerical quantities. A percent is a special type of ratio where the second value is always 100.

Definition: A percent is ratio where n percent, denoted as n%, is the ratio n : 100. That is, a ratio compares numerical quantities in terms of the number of parts out of 100.

Note that the word percent is a statement of a ratio relationship and English "per cent" is derived from Latin "per centum" which means "per hundred". We use the root cent in many words in the English language.

Examples:

A century is 100 years.

Centigrade is the temperature scale where 0° is the freezing point and 100° is the boiling point of water.

A cent is a penny which is one hundredth of a dollar.

A centimeter 0.01 of a meter.  

When we have 17 parts out of 100 (or part to whole ratio 17 : 100), we have 17%. The symbol % is called the percent sign. The expression 17% means 17 parts out of 100. Therefore, 17% is equivalent to the common fraction and to the decimal fraction 0.17. We model 17% as the shaded area in a 10 × 10 grid in which 17 out of the 100 squares have been shaded.  

Self-Check Problem

What percent of each figure is shaded?

First Grid Second Grid Third Grid

return to top | next page