When you deposit money into an account at a bank, there is typically an interest rate applied to the amount you maintain in that account. The interest paid to you is a percent of your balance that the bank rewards you for keeping your money with them. The bank can then use that money as loans to other customers and collect interest on those loans. Calculating interest and working with interest equations are a little trickier than the equations we solved in the last section. The ability to manipulate complex equations like the interest formula is an important skill, as you will then be able to solve equations for any unknown.