# Average Calculator

* SD = standard deviation

## Weighted average calculator

## Average calculation

The average (arithmetic mean) is equal to the sum of the n numbers divided by n:

*Average*=

*=*

sumcount

*a*

_{1}+

*a*

_{2}+...+

*a*

_{n}*n*

#### Example

The average of 1,2,5 is:

*Average*=

1+2+53

= 2.667## Weighted average calculation

The weighted average (*x*) is equal to the sum of the product of the weight (w_{i}) times the data number (x_{i}) divided by the sum of the weights:

#### Example

Find the weighted average of class grades (with equal weight) 70,70,80,80,80,90:

Since the weight of all grades are equal, we can calculate these grades with simple average or we can cound how many times each grade apear and use weighted average.

2×70,3×80,1×90

*x*=

2×70+3×80+1×902+3+1

= 4706

= 78.33333