Percent

The term percent represents per hundred or divided by one hundred such as

2% = 2/100 and
35% = 35/100

In order to find x% of y, where x and y are real numbers, we multiply x% with y. For example,

30% of 500 => 30/100 x 500 = 150

On the other hand, in order to find that, x is what %age of y, we divide x and y and multiply it with 100. Here x and y are real numbers. For example,

7 is what percent of 14?
Here 7 is divided by 14 and multiplied by 100
7/14 x 100 = 50 %

If we want to find the %age increase, We can do as follows
Suppose, there is a number 400 which is increased by 50 numbers and becomes 450. We can detect percent increase by this way

50/400 x 100 = 12.5%

In order to detect %age decrease, we can do as follows
Suppose there is a number 200 which is decreased by 20 numbers and becomes 180, we can calculate % decrease by

20/200 x 100 = 10%

To detect %age increase, Suppose x is a number and y is its final increased state (any number) and z = y - x

Here z/x x 100 and to%age decrease , x is a number and y is decreased number and z = x - y, so z/x x 100.

Here x=base.

In the above examples, 400 and 200 are bases.

Further Reading:
Cracking the GRE, 2010 Edition (Graduate School Test Preparation)

Kaplan GRE Exam Vocabulary in a Box

Barron's GRE

Essential Words for the GRE (Barron's Essential Words for the GRE)

Kaplan GRE Exam 2010-2011 Premier with CD-ROM (Kaplan GRE Premier Program (W/CD))

GRE: Practicing to Take the General Test 10th Edition (Practicing to Take the Gre General Test)

Kaplan GRE Exam Math Workbook

Barron's GRE with CD-ROM

Kaplan GRE Exam 2009 Premier Program (w/ CD-ROM) (Kaplan Gre Exam Premier Live)