Suppose that you are the owner of a local sandwich shop. Your supplier of bread has increased its wholesale price by 10 percent, your supplier of condiments has raised prices by 10 percent, and your supplier of meats and vegetables has raised prices by 10 percent. Suppose these are your only supplies. Therefore, you decide to raise your sandwich prices accordingly. If you wish to maintain the same level of profit given the increases in your supply prices, you should increase your sandwich prices by what percentage?

a. 5 percent
b. 30 percent
c. 100 percent
d. 20 percent
e. 10 percent

In general, you add percentages as you would add cadinal numbers.