A percentage is a way of writing a fraction with a denominator of 100. Percentage means "out of 100" or "parts per hundred" Calculations involving percentages often require multiplication or division by 100. x percent, written x%, means ^{x}⁄_{100} (or x parts out of 100) 
To write a number as a percentage you have to know how many hundredths it contains:
Write 34 hundredths as a percentage  34 hundredths = 34% 
Write 3 tenths as a percentage  3 tenths = 30 hundredths = 30% 
Write the fraction ^{7}⁄_{10} as a percentage 
^{7}⁄_{10} = 70 hundredths = 70% 
You should remember these often used percentages:
Percentage 
0%

10%

25%

33%
(approx.) 
50%

67%
(approx.) 
75%

100%

Fraction  nothing 
one
tenth 
one
quarter 
one 
one 
two
thirds 
three quarters

one whole
(everything!) 
Percentage Calculations
Below are some of the types of problem that use percentages.
Percentage of a quantity:
To find x percent of a quantity. Calculate: ^{x}⁄_{100} × (the quantity)
Find 40% of 500 
Write 40% as a fraction OR as a decimal and then multiply it by 500. Either 500 × 0.40 = 200 
One quantity as a percentage of another quantity:
To find a out of b as a percentage. Calculate: ^{a}⁄_{b} × ^{100}⁄_{1}
Write 16 out of 25 as a percentage 
Write 16 out of 25 as a fraction and then multiply it by 100. ^{16}⁄_{25} × ^{100}⁄_{1} = 64% OR Write 16 out of 25 as a fraction and then find the equivalent fraction with a denominator of 100.

Applications


a  In a library, 52% of the books are fiction, 42% are nonfiction and the rest are reference books. If the library has 9000 books how many of each type does it have? 
The percentage of reference books


b 
A man has a total weight of 80 kg. His muscles weigh 32 kg. What percentage of his weight is muscle? 
Percentage of muscle = 32/ 80 = 40%  
c

A sausage weighs 96 grams and 15% of the sausage is fat. How many grams of fat are there in the sausage?

Weight of fat = 96 × 0.15 = 14.4 grams

Further Work on Percentages
There are several other types of calculations that use percentages and these are covered in other topics:
Conversions  Fractions <> Decimals <> Percentages.  
Harder Number Work  Includes percentage increase and decrease, profit and loss and discounts. 
