Mean

To find the Mean:
Add up all the values and divide by how many values there are.

Eg:

1,1,4,5,5,5,

1 + 1 + 4 + 5 + 5 + 5 + =  21
   
21 divided by 7 = 3



http://chemistry.about.com/od/workedchemistryproblems/a/calculate-the-mean.htm