Average Calculator
An average or arithmetic mean is a calculated "central" value of a set of numbers. To calculate it: sum up all the numbers, then divide by how many numbers there are.
What Is An Average
An average is a single number taken as representative of a list of numbers. Different concepts of average are used in different contexts. Often "average" refers to the arithmetic mean, the sum of the numbers divided by how many numbers are being averaged.
Average = 

Sum of all numbers: It is a result of adding all the given numbers
Total number count: It is the number of values being added.
For example, given the 5 numbers, 15, 5, 30, 4, and 2, the average can be calculated as such:
 = 11.2 
Arithmetic Mean
The most common type of average is the arithmetic mean. If n numbers are given, each number denoted by ai (where i = 1,2, ..., n), the arithmetic mean is the sum of the as divided by n
Geometric Mean
The geometric mean of n positive numbers is obtained by multiplying them all together and then taking the nth root.
Median
Median is the middle number in a sorted list of numbers. To determine the median value in a sequence of numbers, the numbers must first be sorted, or arranged, in value order from lowest to highest or highest to lowest.
Range
The difference between the largest and smallest data in a data set. To figure the range subtract the smallest number from the largest number 30  2 = 28.