Middel so lets say you have a group of numbers such as this group below
18 , 20 , 34 , 15 , 78 , 100 , 12 , 46 , 89
You put those #s is order from smallest to largest like this
12 , 15 , 18 , 20 ,...
The mean of a series of numbers is the average - calculated by added all the numbers in the series and dividing the sum by the number of numbers in the series. Given the set of numbers {1,2,3,4,5},...