Click the cell where the result appears
Click the Layout tab under Table Tools.
Click the Formula button.
Click the Paste Function list arrow
Then select a function.
To average the values in cells a1 through a4, the formula would be =Average(a1,a4).
For the average of a row in the last column of the row, the formula would be =Average(left)
In the Number format box, enter a format for the numbers.
To display a decimal percentage, click 0.00%.
To display a average, enter 0.00 in the Number Format box.