Question

If the simple interest on $5,000 for 9 years is $1,800, then what is the interest rate?

The rate is %.

Answer 1

`I = Prt\qquad \begin{cases} I=\textit{interest earned}\dotfill & \$1800\\ P=\textit{original amount deposited}\dotfill & \$5000\\ r=rate\to r\%\to (r)/(100)\\ t=years\dotfill &9 \end{cases} \\\\\\ 1800=5000((r)/(100))(9)\implies \cfrac{1800}{5000(9)}=\cfrac{r}{100}\implies \cfrac{1}{25}=\cfrac{r}{100} \\\\\\ 100=25r\implies \cfrac{100}{25}=r\implies \stackrel{\%}{4}=r`