Percents
Like fractions and decimals, percents are a way of representing
part of something.
Why do we use percentages? It is a simple and convenient way to
use ratios. It is easier to say â€œfive percentâ€ than â€œzero point zero
five of the totalâ€.
You can use percents anywhere ratios are used, and thatâ€™s just about everywhere!
Here are some examplesâ€¦
Percents can compare groups.
Percents can predict the future.
Percents can simplify many numbers.
Percents are particularly useful with money.
Percent
Percent or % is a special ratio that means a number of parts â€œper one hundredâ€. It is a
standard of measure.
Examples:
10% may be written as
25% may also be written as
99% is written as
125% may be written as
Definitions:
Base  is the whole quantity
Percentage  is the portion of the whole quantity
Rate  is the percent (%), think of â€œratioâ€ when you see this!
Percents may be added, subtracted, multiplied or divided in the same way as other ratios.
Example: 8% + 6% = 14%
Example: 18%  12% = 6%
Example: 18% Ã· 9 = 2%
Example: 7% Ã— 5 = 35%
Converting percents to decimals
To change a percent to a decimal, remove the percent sign and move the decimal point two
places to the left (divide by 100).
Example: Change 25% to a decimal
Example: Change 200% to a decimal
Converting decimals to percents
To change a decimal to a percent, multiply by 100 (move the decimal point two places to the
right) and write the percent sign:
Example: Change 0.057 to a percent
0.057 = 5.7 %
Example: Change 2.43 to a percent
2.43 = 243%
Computing percentages and percents
Example: What is 8% of 50 ?
Solution: The rate or percent is 8%. The base or whole quantity is 50.
Remember that a â€œpercentâ€ is the same as a ratio.
Also recall that â€œofâ€ is the same as multiplying.
First, convert the percent to a decimal:
8% = 0.08
Next, multiply the decimal by the base:
50 Ã— 0.08 = 4
Answer: 8% of 50 is 4
Example: 25 is what percent of 50?
Solution: To solve a â€œwhat percentâ€ problem, we must find the ratio.
Here the base or whole quantity is again 50.
The percent or part of the whole quantity is 25.
To solve for the percent, divide the percent 25 by the base 50.
Now convert the decimal fraction 0.5 into percent by multiplying by 100 and
writing %:
