Bài 1: Gọi p/s đó là: \(\frac{x}{13}\left(x\in Z\right)\)
Ta có: \(\frac{x+-20}{13.5}=\frac{x}{13}\) (1)
\(\frac{x.5}{13.5}=\frac{x}{13}\) (2)
Từ (1) và (2) \(\Rightarrow\) x.5 = x+-20
\(\Leftrightarrow\) 5x=x-20
\(\Leftrightarrow\) 5x-x=-20
\(\Leftrightarrow\) 4x=-20
\(\Leftrightarrow x=-20:4=-5\)
Vậy p/s đó là: \(\frac{-5}{13}\)
Bài 2: a)
Ta có: \(\left\{{}\begin{matrix}x+y=425\\y-x=153\end{matrix}\right.\)
\(\Rightarrow\)x+y+y-x=425+153
\(\Leftrightarrow\) (y+y)+(x-x)=578
\(\Leftrightarrow2y=578\)
\(\Leftrightarrow y=578:2=289\)
\(\Rightarrow x=\) 425-289=136
Vậy:
\(\frac{x}{y}=\)\(\frac{136}{289}\)