We sometimes need to find how long it will take a sum of money (or anything else) to grow to some specified amount. Note that you should enter PV as a negative and FV as a positive. For example, if a companys sales are growing at a rate of 5.90% per year, approximately how long will it take sales to double? Show your answer to 2 decimals (x.xx years). If you are not sure how to work this, go back to this weeks practice problems. Do not approximate using the rule of 72. If you are in doubt here, go back to the practice problems where double/tripling is discussed. (b) If you want an investment to triple in eighteen years, what interest rate must it earn? Show your answer to 2 decimals (x.xx%)