A percentage is a way of expressing a decimal number or fraction. For instance, you can write the decimal 0.25 as 25 per cent, 0.05 as 5 per cent and 1.0 as 100 per cent. MS Excel 2007 provides tools for calculating decimals, and you may format any decimal number with a per cent sign (%). Since cell formatting only changes the number's appearance, you can use percentages in mathematical formulas.

Format a cell to display a percentage. In Excel, type a decimal value into cell A1, such as 0.3. Press "Enter." On the "Home" tab of the ribbon, in the "Number" section, click "%" to display 30%."

Calculate a percentage. If you have 100 boxes and 12 of them are red, find the percentage of red boxes by dividing the amount,12, by the total, 100. In Excel, enter the following:

Cell A1: 12 Cell A2: 100 Cell A3: =A1/A2

In cell A3, press "Enter" to view the result, 0.12. Format cell A3 as a percentage---as in Step 1---to display "12%."

Figure the amount of a percentage. If you are buying a camera for £97 and you want to find how much a 5 per cent sales tax will be, multiply the total, 150 by the decimal that represents the percentage (divided the per cent, 5, by 100), 0.05. In Excel, enter the following:

Cell B1: 150 Cell B2: .05 Cell B3: =B1*B2

In cell B3, press "Enter" to see the result, 7.5. To show the value as a dollar amount, format cell B3 as currency. On the "Home" tab of the ribbon, in the "Number" section, click "$" to display "$7.50."

Find the original amount from a total that has been reduced by a percentage. If you are shopping for shirts at 30 per cent off and the reduced price is £13, calculate the original price by dividing the discounted price, 21, by the difference between 100 per cent and the 30 per cent discount (1 minus 0.3), in this case 0.7. In Excel, enter the following:

Cell C1: 21 Cell C2: .7 Cell C3: =C1/C2

In cell C3, press "Enter" to see the original price, 30. Format cell C3 as currency to display "$30.00."

Increase a total by a percentage. If you get a 3 per cent raise and your salary is £31,200, figure your new salary by multiplying your current yearly wages, 48,000, by 1 plus the percentage of the increase (1 plus 0.03), 1.03. In Excel, enter the following:

Cell D1: 48000 Cell D2: 1.03 Cell D3: =D1*D2

In cell D3, press "Enter" to see your new salary, 49,440. Format cell D3 as currency to display "$49,440.00."

Decrease a total by a percentage. If your monthly entertainment expenses are £65 and you want to reduce expenditure by 5 per cent, multiply your current budget, 100, by 1 minus the percentage of the decrease (1 minus 0.05), or 0.95 in this example. In Excel, enter the following:

Cell E1: 100 Cell E2: .95 Cell E3: =E1*E2

In cell E3, press "Enter" to view your revised entertainment budget, 95. Format cell E3 as currency to display "$95.00."

#### Tip

The error message "#DIV/0!" means that you tried to divide a number by zero. If a cell displays "#####," the column is not wide enough to show the value. Double-click the column divider to adjust the column width. If your cell formatting limits display to only a few decimal places, the values will still be correct, but they will appear to be rounded. For instance, 25.006 formatted as currency looks like "$25.01." In some cases, using these values in calculations will give results that look inaccurate. If you need a precise display, use a general number format.