\[\boxed{\text{11.\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[\boxed{\text{1.\ }}\]
\[\boxed{\text{2.\ }}\]
\[\boxed{\text{3.\ }}\]
\[4 < a < 5;\ \ \ \ \ \ 9 < b < 10\]
\[1) + \left| \begin{matrix} 4 < a < 5 \\ 9 < b < 10 \\ \end{matrix} \right.\ \]
\(\overline{13 < a + b < 15}\)
\[2) + \left| \begin{matrix} \ \ \ \ 4 < a < 5\ \\ - 10 < - b < - 9 \\ \end{matrix} \right.\ \]
\[\text{\ \ \ \ \ }\overline{\ - 6 < a - b < - 4}\]
\[3)*\left| \begin{matrix} 4 < a < 5 \\ 9 < b < 10 \\ \end{matrix} \right.\ \]
\[\text{\ \ \ \ \ \ }\overline{\ \ \ 36 < ab < 50}\]
\[4)\ \frac{a}{b} = a \cdot \frac{1}{b}\]
\[*\left\{ \begin{matrix} \frac{1}{10} < \frac{1}{b} < \frac{1}{9} \\ 4 < a < 5 \\ \end{matrix} \right.\ \]
\[\text{\ \ \ \ }\overline{\frac{4}{10} < \frac{a}{b} < \frac{5}{9}}\]