Let r be the percent annual interest rate of the account. Since $9000 are left for 5 years, for an outcome of $12,500, then:
[tex]9000\times(1+\frac{r}{100})^5=12,500[/tex]Divide both sides by 9000:
[tex](1+\frac{r}{100})^5=\frac{12500}{9000}=\frac{25}{18}[/tex]Take the 5th root to both sides:
[tex]\begin{gathered} 1+\frac{r}{100}=\sqrt[5]{\frac{25}{18}} \\ \Rightarrow\frac{r}{100}=\sqrt[5]{\frac{25}{18}}-1 \\ \Rightarrow r=100(\sqrt[5]{\frac{25}{18}}-1) \end{gathered}[/tex]Use a calculator to find the decimal expression for r:
[tex]r=6.790716585\ldots[/tex]Therefore, to the nearest tenth:
[tex]r=6.8[/tex]This means that Joshua would need to invest his money on a 6.8% annual interest account.
