Using AutoSum
Because SUM is one of the most commonly used functions, Excel provides a fast way to enter it—you simply click the AutoSum button in the Standard toolbar. Based on the currently selected cell, AutoSum guesses which cells you want summed. If AutoSum selects an incorrect range of cells, you can edit the selection.
To use AutoSum, follow these steps:
Select the cell in which you want the sum inserted. Try to choose a cell at the end of a row or column of data; doing so will help AutoSum guess which cells you want added together.
Click the AutoSum button in the Standard toolbar. AutoSum inserts =SUM and the range address of the cells to the left of or above the selected cell (see Figure 16.1).Figure 16.1. AutoSum inserts the SUM function and selects the cells it plans to total.
If the range Excel selected is incorrect, drag over the range you want to use, or click in the Formula bar and edit the formula.
Click the Enter button in the Formula bar or press Enter. Excel calculates the total for the selected range.
Quickie AutoSum
To quickly insert the SUM function, select the cell in which you want the sum inserted and double-click the AutoSum tool on the Standard toolbar. When you double-click the AutoSum button instead of single-clicking, you bypass the step where Excel displays the SUM formula and its arguments in the cell. Instead, you see the total in the cell and the SUM formula in the Formula bar. Of course, the problem with using this method is that you're not given a chance to "second-guess" the range of cells AutoSum decides to add.