Đáp án:

$818,2\left( {kg/{m^3}} \right)$

Giải thích các bước giải:

 Theo đề bài ta có:

$\begin{array}{l}
\Delta V = 0,002{V_0} \Rightarrow \frac{{\Delta V}}{{{V_0}}} = \beta .\Delta t \Rightarrow \beta  = 0,002\\
\Delta {V_1} = \beta .\Delta t{V_0} = 0,002.50.{V_0}\\
{V_1} = {V_0} + \Delta {V_1} = 1,1{V_0} \Rightarrow \frac{{{V_0}}}{{{V_1}}} = \frac{1}{{1,1}}\\
{D_1} = \frac{m}{{{V_1}}};{D_0} = \frac{m}{{{V_0}}}\\
\frac{{{D_1}}}{{{D_0}}} = \frac{{{V_0}}}{{{V_1}}} \Rightarrow \frac{{{D_1}}}{{900}} = \frac{1}{{1,1}} \Rightarrow {D_1} = 818,2\left( {kg/{m^3}} \right)
\end{array}$