Question

Sam opened a money-market account that pays 3% simple interest. He started the account with $7,000 and made no further deposits. When he closed the account, he had earned $420 in interest. How long did he keep his account open?

Answer 1

he kept the account open for 2 years

Explanation:

Answer 2

`\bf ~~~~~~ \textit{Simple Interest Earned} \\\\ I = Prt\qquad \begin{cases} I=\textit{interest earned}\dotfill&420\\ P=\textit{original amount deposited}\dotfill & \$7000\\ r=rate\to 3\%\to (3)/(100)\dotfill &0.03\\ t=years \end{cases} \\\\\\ 420=(7000)(0.03)t\implies \cfrac{420}{(7000)(0.03)}=t\implies 2=t`