A function is a predefined formula that helps save you time. For example, use the SUM function to add lots of numbers or cells, and the PRODUCT function to multiply them.

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**AutoSum** makes it easy to add adjacent cells in rows and columns.

You could type out =A3+A4+A5+A6, but that is tedious.

Instead, click the cell to the right of a row or below a column.

Then, on the **HOME** tab, click **AutoSum**, verify that the formula is what you want, and click **AutoSum** again.

**AutoSum** adds the row or column automatically. It is really handy.

When I double-click inside a cell where I am using **AutoSum**, I see it is a formula with the **SUM** function.

A function is a predefined formula. It helps save you time.

The syntax, or grammar, of the **SUM** function is **SUM**, open parenthesis, arguments--like numbers or cell references separated by commas--and finally, close parenthesis.

This formula is **SUM**(A3:A6).

The colon indicates a range of cells. This formula adds the cells from A3 through A6.

When adding a few cells, the **SUM** function saves you time.

With larger ranges of cells, it is essential.

If you try to use **AutoSum** here, it only gets the adjacent cell, not the entire column.

Why? Because B5 is empty.

If B5 wasn't empty, B3 through B6 would be an adjacent range of cells that **AutoSum** could recognize.

To add cells and ranges of cells that aren't adjacent: **SUM**, hold down the Ctrl key, click the desired cells and ranges of cells, and press Enter.

The formula uses the **SUM** function to add the cells containing numbers and ignores the empty cells.

Subtraction is similar to addition, but there isn't a subtraction function.

To subtract, you use a basic formula like: number or cell, minus, the next number or cell, and so on.

You can **SUM** numbers where some of them are negative.

The keyboard shortcut for **AutoSum** is Alt+=, and then I press Enter.

This is equivalent to 6 - 3 + 4 - 5.

You can also subtract the results of one **SUM** function from another.

**SUM**, select a range of cells, minus, **SUM**, select another range of cells, and press Enter.

As I mentioned about adding earlier, to multiply cells, you could type out =A3*A4*A5*A6, but that is tedious.

To speed things up, use the **PRODUCT** function to multiply numbers or cells.

**PRODUCT** is similar to the **SUM** function, but instead of adding numbers, it multiplies them.

It is another example of how functions help save you time.

The syntax of the **PRODUCT** function is **PRODUCT**, open parenthesis, arguments--like numbers or cell references separated by commas--and finally, close parenthesis.

To multiply cells and ranges of cells in one formula: **PRODUCT**, hold down the Ctrl key, select the desired cells and ranges of cells, and press Enter.

The formula uses the **PRODUCT** function to multiply cells containing numbers and ignores the empty cells.

Division is similar to multiplication, but there isn't a divide function.

A basic formula would be: number or cell, /, the next number or cell, and so on.

You can divide the results of one function, such as **PRODUCT**, by the results of another, such as **SUM**.

This formula divides the **PRODUCT** of the cells in B3 through B6, by the **SUM** of the cells in C3 through C6.

Up next, **Operator order**.