Explanation:

Addition is a mathematical operation that represents combining collections of objects together into a larger collection. It is signified by the plus sign (+). For example, in the picture on the right, there are 3 + 2 apples-meaning three apples and two other apples-which is the same as five apples. Therefore, 3 + 2 = 5 (Our solved example in mathguru.com uses this concept)

Besides counting fruits, addition can also represent combining other physical and abstract quantities using different kinds of numbers: negative numbers, fractions, irrational numbers, vectors, decimals and more.

3 + 2 = 5 with apples

http://en.wikipedia.org/wiki/Addition

In mathematics, a variable is a value that may change within the scope of a given problem or set of operations. (Our solved example in mathguru.com uses this concept)

http://en.wikipedia.org/wiki/Variable_(mathematics)

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.