\(\mathrm{v}_2=\text { volume immersed in oil. }\)
\(\mathrm{v}_1 \rho_{\mathrm{w}} \mathrm{g}+\mathrm{v}_2 \rho_{\mathrm{o}} \mathrm{g}=\left(\mathrm{v}_1+\mathrm{v}_2\right) \rho_{\mathrm{c}} \mathrm{g}\)
\(\mathrm{v}_1+\frac{\mathrm{v}_2 \rho_0}{\rho_w}=\left(\mathrm{v}_1+\mathrm{v}_2\right) \frac{\rho_{\mathrm{c}}}{\rho_w}\)
\(=\mathrm{v}_1+0.8 \mathrm{v}_2=0.9 \mathrm{v}_1+0.9 \mathrm{v}_2\)
\(=0.1 \mathrm{v}_1=0.1 \mathrm{v}_2\)
\(\mathrm{v}_1: \mathrm{v}_2=1: 1\)