Chapter Outline

Percent

A percent, like a decimal or a fraction, describes a part of a whole.

• With percent, one whole is always divided into 100 parts.
• A percent is indicated with the % sign.
• Percent can be expressed as a two-place decimal (hundredths) or as a fraction with a denominator of 100.

Understanding Percent

One whole is 100%.

• A percent greater than 50% is greater than ½.
• A percent less than 50% is less than ½.
• A percent greater than 100% is greater than one whole.

Percents, Decimals, and Fractions

To change a percent to a decimal, follow these steps:

• Drop the % sign.
• Move the decimal point two places to the left.

To change a decimal to a percent, follow these steps:

• Move the decimal point two places to the right.
• Write the percent sign after the last digit.

To change a percent to a fraction, follow these steps:

• Drop the % sign.
• Write 100 as the denominator.
• Reduce.

To change a fraction to a percent, multiply the fraction by 100%.

Solving Percent Problems

Finding a percent of a number means finding the part. To find a percent of a number, follow these steps:

• Change the percent to a decimal or a fraction.
• Multiply.

Finding what percent one number is of another means finding the percent. To find what percent one number is of another, follow these steps:

• Make a fraction with the part over the whole.
• Reduce.
• Change the fraction to a percent.

Finding a number when a percent of it is given means finding the whole. To find a number when a percent of it is given, follow these steps:

• Change the percent to either a fraction or a decimal.
• Divide the number by that fraction or decimal.

Percent Word Problems

A rate of change compares an amount of change to an original amount. To calculate a rate of change, follow these steps:

• Find the amount of change.
• Put the change in the numerator and the original amount in the denominator.
• Multiply by 100%.

Interest is money that money makes. The formula for calculating interest is interest = principal × rate × time.

• Principal is the amount of money that is borrowed or saved.
• Rate is the percent.
• Time is the period (usually measured in years) that the principal is saved or borrowed.