Question

Diana invested $3000 in a savings account for 3 years. She earned $450 in interest over that time period. What interest rate did she earn? Use the formula I=Prt to find your answer, where I is interest, P is principal, r is rate and t is time. Enter your solution in decimal form rounded to the nearest hundredth. For example, if your solution is 12%, you would enter 0.12.

Answer 1

$\bf ~~~~~~ \textit{Simple Interest Earned} \\\\ I = Prt\qquad \begin{cases} I=\textit{interest earned}\to &\ 450\\ P=\textit{original amount deposited}\to& \ 3000\\ r=rate\to r\%\to \frac{r}{100}\\ t=years\to &3 \end{cases} \\\\\\ 450=(3000)(r)(3)\implies \cfrac{450}{(3000)(3)}=r\implies \cfrac{1}{20}=r \\\\\\ 0.05=r\implies r\%=0.05\cdot 100\implies r=\stackrel{\%}{5}$