Question

How long will it take Thomas to double his $3,500 in an account that pays 6.9% simple interest ?

Answer 1

`~~~~~~ \textit{Simple Interest Earned Amount} \\\\ A=P(1+rt)\qquad \begin{cases} A=\textit{accumulated amount}\dotfill & \stackrel{ double }{\$ 7000}\\ P=\textit{original amount deposited}\dotfill & \$3500\\ r=rate\to 6.9\%\to (6.9)/(100)\dotfill &0.069\\ t=years \end{cases} \\\\\\ 7000 = 3500[1+(0.069)(t)] \implies \cfrac{7000}{3500}=1+0.069t\implies 2=1+0.069t \\\\\\ 1=0.069t\implies \cfrac{1}{0.069}=t\implies 14.49\approx t\qquad \textit{about 14 years and a half}`