Ta có : \(\left[ \begin{array}{l}5.2=10\\4.5=20\end{array} \right.\)
\(\left[ \begin{array}{l}2.5=10\\x=5.4=20\end{array} \right.\)
\(\left[ \begin{array}{l}10.1=10\\10.2=20\end{array} \right.\)
\(\left[ \begin{array}{l}1.10=10\\2.10=20\end{array} \right.\)
`=>5/4 . 2/5 = 5/4:5/2=10/20`
`2/5 . 5/4 = 2/5 : 4/5=10/20`
`10/10 . 1/2 = 10/10 : 2/1=10/20`
`1/2 . 10/10 = 1/2 : 10/10 = 10/20`
Vậy `2` cách viết đó là : `5/4:2/5=10/20` và `10/10:2/1=10/20`