\[x - рабочих;\ \]
\[y - дней.\]
\[\left\{ \begin{matrix} - 5x + 10y = 50\ \ \ \ \ (1) \\ 10x - 10y = 100\ \ \ \ (2) \\ \end{matrix} \right.\ \]
\[(1) + (2):\ \ \ 5x = 150\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x = 30\]
\[Ответ:30\ человек.\]