\(Đặt.CTTQ:Ca_pC_zO_r\left(p,z,r:nguyên,dương\right)\\ Vì:m_{Ca}:m_C:m_O=1:0,3:1,2\\ \Leftrightarrow40p:12z:16r=1:0,3:1,2\\ \Leftrightarrow p:z:r=\dfrac{1}{40}:\dfrac{0,3}{12}:\dfrac{1,2}{16}=\dfrac{1}{40}:\dfrac{1}{40}:\dfrac{3}{40}=1:1:3\\ \Rightarrow p=1;z=1;r=3\\ \Rightarrow CTHH:CaCO_3\)