Notăm:
b - numărul băieților;
f - numărul fetelor.
[tex]\it b+f=33 \Rightarrow b=33-f\ \ \ \ \ (1)\\ \\ \dfrac{2}{3}b=\dfrac{1}{4}f \Rightarrow b=\dfrac{1}{4}\cdot\dfrac{3}{2}f \Rightarrow b=\dfrac{3}{8}f\ \ \ \ \ (2)\\ \\ \\ (1),\ (2) \Rightarrow \dfrac{3}{8}f=33-f\Big|_{\cdot8} \Rightarrow 3f=8\cdot33-8f\Big|_{+8f} \Rightarrow \\ \\ \\ \Rightarrow11f=8\cdot33|_{:11} \Rightarrow f=8\cdot3 \Rightarrow f=24\ \ \ \ \ (3)\\ \\ \\ (1),\ (3) \Rightarrow b=33-24=9[/tex]
