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

#### Step

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%.”

#### Step

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:

#### Step

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

#### Step

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

#### Step

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

#### Step

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

#### Step

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."

#### Step

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

#### Step

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

#### Step

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

#### Step

Increase a total by a percentage. If you get a 3 percent raise and your salary is $48,000, 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:

#### Step

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

#### Step

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

#### Step

Decrease a total by a percentage. If your monthly entertainment expenses are $100 and you want to reduce expenditure by 5 percent, 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:

#### Step

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

#### Step

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