Question

mr.johnson borrowed $8000 for 4 years to make home improvements. if he repaid a total of $10,320, what interest rate did he borrow the money?

Answer 1

R=(10320/8000)^(1/4))-1)*100
R=6.6%

Answer 2

$\bf \qquad \textit{Simple Interest Earned Amount}\\\\ A=P(1+rt)\qquad \begin{cases} A=\textit{compounded amount}\to &10,320\\ P=\textit{original amount }\to& \ 8000\\ r=rate\\ t=years\to &4 \end{cases}$

plug in the values, and solve for "r"

you'll get a decimal amount, so multiply it by 100, to get the percentage figure for the rate used