Explanation:
In mathematics, a percentage is a way of expressing a
number as a fraction of 100 (per cent meaning "per
hundred" in Latin). It is often denoted using the percent sign, "%",
or the abbreviation "pct". For example, 45% (read as "forty-five
percent") is equal to 45/100, or 0.45. (Our solved example in
mathguru.com uses this concept)
Percentages
are used to express how large/small one quantity is, relative to another
quantity. The first quantity usually represents a part of, or a change in, the
second quantity, which should be greater than zero. For example, an increase of
\($\) 0.15 on a price of \($\) 2.50 is an increase by a fraction of 0.15/2.50
= 0.06. Expressed as a percentage, this is therefore a 6% increase.
Calculations
The fundamental concept to remember when performing calculations
with percentages is that the percent symbol can be treated as being equivalent
to the pure number constant1 / 100 = 0.01 , for example 35% of 300 can be written as (35/100) × 300 = 105. (Our solved example in
mathguru.com uses this concept)
To find the percentage that a single unit represents out of a
whole of N units, divide 100% by N. For instance, if you have 1250 apples, and
you want to find out what percentage of these 1250 apples a single apple
represents, 100%/1250 =
(100/1250)% provides the answer
of 0.08%. So, if you give away one apple, you have given away 0.08% of the
apples you had. Then, if instead you give away 100 apples, you have given away
100 × 0.08% = 8% of your 1250 apples.
To calculate a percentage of a percentage, convert both
percentages to fractions of 100, or to decimals, and multiply them. For
example, 50% of 40% is:
(50/100)
× (40/100) = 0.50 × 0.40 = 0.20 = 20/100 = 20%.
It is not correct to divide by 100 and use the percent sign at the
same time. (E.g. 25% = 25/100 =
0.25, not 25% / 100, which
actually is (25/100) / 100 =
0.0025.)
http://en.wikipedia.org/wiki/Percentage
The above explanation is copied from
Wikipedia, the free encyclopedia and is remixed as allowed under the Creative
Commons Attribution- ShareAlike 3.0 Unported License.