[tex]~~~~~~ \textit{Simple Interest Earned} \\\\ I = Prt\qquad \begin{cases} I=\textit{interest earned}\dotfill & \$5\\ P=\textit{original amount deposited}\\ r=rate\to 1.25\%\to \frac{1.25}{100}\dotfill &0.0125\\ t=years\dotfill &\frac{1}{2} \end{cases} \\\\\\ 5 = (P)(0.0125)(\frac{1}{2})\implies \cfrac{5}{(0.0125)(\frac{1}{2})}=P\implies 800=P[/tex]
