Question

Do Xuan nam isgoing to invest $1000 at a simple interest rate of 4% how long will it take for the investment to be worth $1040?

Answer 1

$\bf ~~~~~~ \textit{Simple Interest Earned Amount} \\\\ A=P(1+rt)\qquad \begin{cases} A=\textit{accumulated amount}\dotfill&\ 1040\\ P=\textit{original amount deposited}\dotfill & \ 1000\\ r=rate\to 4\%\to \frac{4}{100}\dotfill &0.04\\ t=years \end{cases} \\\\\\ 1040=1000(1+0.04t)\implies \cfrac{1040}{1000}=1+0.04t\implies \cfrac{26}{25}=1+0.04t \\\\\\ \cfrac{26}{25}-1=0.04t\implies \cfrac{~~\frac{26}{25}-1~~}{0.04}=t\implies \cfrac{~~\frac{1}{25}~~}{0.04}=t\implies 1=t$