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.

$($a$)$ For example, if a company's sales are growing at a rate of $5\mathrm{.}28\%$ per year, 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 week's practice problems. Do not approximate using the "rule of $"72".$ If you are in doubt here, go back to the lecture notes and practice problem $6$ where double tripling is discussed. Read the notes!

$($b$)$ If you want an investment to triple in fourteen years, what interest rate must it earn? Show your answer to $2$ decimals $(x.\%).$