Đáp án + giải thích các bước giải:
$\left\{\begin{matrix} x+\dfrac{1}{3}y=30\\\dfrac{1}{2}x+y=30 \end{matrix}\right. \\ \to \left\{\begin{matrix} x+\dfrac{1}{3}y=30\\x+2y=60 \end{matrix}\right. \\ \to \left\{\begin{matrix} x+2y-x-\dfrac{1}{3}y=60-30\\x+2y=60 \end{matrix}\right. \\ \to \left\{\begin{matrix} \dfrac{5}{3}y=30\\x+2y=60 \end{matrix}\right. \\ \to \left\{\begin{matrix} y=18\\x=24 \end{matrix}\right.$