Ta có ;
\(\dfrac{4}{5}x=\dfrac{6}{5}y\) \(\Leftrightarrow\) \(\dfrac{x}{\dfrac{6}{5}}=\dfrac{y}{\dfrac{4}{5}}=\dfrac{x-y}{\dfrac{6}{5}-\dfrac{4}{5}}=\dfrac{6}{\dfrac{2}{5}}=15\)
\(\Rightarrow\left[{}\begin{matrix}\dfrac{x}{\dfrac{6}{5}}=15\\\dfrac{y}{\dfrac{4}{5}}=15\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=18\\y=12\end{matrix}\right.\)
Vậy số lớn nhất cần tìm là 18