Đáp án:
\(\begin{array}{l}
a.\\
{D_A} = 18{D_B}\\
b.\\
D = \frac{4}{{21}}{D_A} = \frac{{24}}{7}{D_B}
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
a.\\
\frac{{{D_A}}}{{{D_B}}} = \frac{{\frac{{{m_A}}}{{{V_A}}}}}{{\frac{{{m_B}}}{{{V_B}}}}} = \frac{{\frac{{3{m_B}}}{{{V_A}}}}}{{\frac{{{m_B}}}{{6{V_A}}}}} = 18\\
{D_A} = 18{D_B}\\
b.\\
\frac{D}{{{D_A}}} = \frac{{\frac{{{m_A} + {m_B}}}{{{V_A} + {V_B}}}}}{{\frac{{{m_A}}}{{{V_A}}}}} = \frac{{\frac{{{m_A} + \frac{1}{3}{m_A}}}{{{V_A} + 6{V_A}}}}}{{\frac{{{m_A}}}{{{V_A}}}}} = \frac{4}{{21}}\\
D = \frac{4}{{21}}{D_A} = 18.\frac{4}{{21}}{D_B} = \frac{{24}}{7}{D_B}
\end{array}\)