\[x - мальчиков;\ \ y - девочек.\]
\[\left\{ \begin{matrix} x + y = 24\ \ \ \ \ | \cdot 2 \\ 3y + 2x = 59\ \ \ \ \ \ \ \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} 2x + 2y = 48 \\ 2x + 3y = 59 \\ \end{matrix} \right.\ \text{\ \ }( - )\]
\[\overline{\ \ \ - y = - 11\ \ \ \ \ \ }\]
\[\ \ \ \ \ \ y = 11\]
\[\left\{ \begin{matrix} y = 11\ \ \ \ \ \ \ \ \ \ \\ 11 + x = 24 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} y = 11 \\ x = 13 \\ \end{matrix} \right.\ \]
\[Ответ:\ 13\ мальчиков,\ \]
\[11\ девочек.\]