\(\dfrac{x}{y}=\dfrac{9}{10}\)

\(\Rightarrow\dfrac{y}{10}=\dfrac{x}{9}\)

Áp dụng t/c dãy tỉ số bằng nhau ta có:

\(\dfrac{y}{10}=\dfrac{x}{9}=\dfrac{y-x}{10-9}=\dfrac{120}{1}=120\)

\(\Rightarrow\left\{{}\begin{matrix}y=120.10=1200\\x=120.9=1080\end{matrix}\right.\)