Em tham khảo nha:
\(\begin{array}{l}
CTHH:F{e_x}{O_y}\\
\% {m_{Fe}} = 100 - 30 = 70\% \\
x:y = \dfrac{{70}}{{56}}:\dfrac{{30}}{{16}} = 2:3\\
\Rightarrow CTHH:F{e_2}{O_3}\\
CTHH:F{e_a}{O_b}\\
\% {m_{Fe}} = 100 - 27,58 = 72,42\% \\
a:b = \dfrac{{72,42}}{{56}}:\dfrac{{27,58}}{{16}} = 3:4\\
\Rightarrow CTHH:F{e_3}{O_4}
\end{array}\)