Originally Posted by
Jhevon use the compound interest formula:
$\displaystyle A = P \left( 1 + \frac rn \right)^{nt}$
where $\displaystyle A$ is the amount after time $\displaystyle t$, $\displaystyle P$ is the principal, $\displaystyle r$ is the rate of interest, and $\displaystyle n$ is the number of times in is compounded per year
here, $\displaystyle n = 1$ and you need to find $\displaystyle r$. but this is what you want to happen. after 5 years, you want $\displaystyle P$ to become $\displaystyle 2P$. thus you want
$\displaystyle 2P = P \left( 1 + r \right)^5$
now solve for $\displaystyle r$