\(n_{HCl}=0,2.3,5=0,7\left(mol\right)\\ Đặt:n_{CuO}=a\left(mol\right);n_{Fe}=b\left(mol\right)\left(a,b>0\right)\\ a,PTHH:CuO+2HCl\rightarrow CuCl_2+H_2O\\ Fe+2HCl\rightarrow FeCl_2+H_2\\ b,Ta.lập.hpt:\left\{{}\begin{matrix}2a+2b=0,7\\80a+56b=20\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=\dfrac{1}{60}\\b=\dfrac{1}{3}\end{matrix}\right.\\ \Rightarrow m_{Fe}=\dfrac{56}{3}\left(g\right);m_{CuO}=80.\dfrac{1}{60}=\dfrac{4}{3}\left(g\right)\)