Find an average by adding all of the numbers in the series together. If you're trying to find the average number for 7, 8, 10 and 11, for example, add them together to get the total of 36.
Divide the total number by the amount of numbers in the series. Since there were four numbers (7, 8, 10 and 11) that went into the total, divide 36 by 4 to find the average. The average, or mean, of these numbers is 9.
Use a "finding the average" math technique to save money on items like groceries, too. If you're trying to determine the better buy between two cases of water bottles, for example, divide the total price of the case by the number of bottles in the case. This will give you the average price per bottle, which you can then compare to the price per bottle in the other case to discover the most economical buy.