Gọi số học sinh là x
theo đề, ta có:
\(\left\{{}\begin{matrix}x-1\in BC\left(2;3;4;8\right)\\x\in B\left(7\right)\\x< =50\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x-1\in\left\{24;48;72;...\right\}\\x\in\left\{...;35;42;49;...\right\}\\x< =50\end{matrix}\right.\Leftrightarrow x=49\)