Em tham khảo nha:
\(\begin{array}{l}
7)\\
{V_{{C_2}{H_5}OH}} = \dfrac{{10 \times 40}}{{100}} = 4(l)\\
{V_{{\rm{dd}}\,{{15}^0}}} = \dfrac{{4 \times 100}}{{15}} = 26,67(l)\\
8)\\
{V_{{C_2}{H_5}OH}} = \dfrac{{1 \times 25}}{{100}} = 0,25\,l\\
{V_{{\rm{dd}}\,{{10}^0}}} = \dfrac{{0,25 \times 100}}{{10}} = 2,5l\\
{V_{{H_2}O}} = 2,5 - 1 = 1,5l = 1500ml\\
9)\\
{V_{{C_2}{H_5}OH}} = 330 \times \dfrac{{4,5}}{{100}} \times 2 = 29,7ml
\end{array}\)