Viết tiếp vào chổ trống:

$$\begin{gathered} Nhận xét:\frac{2}{3}\times \frac{4}{5}=...,\frac{4}{3}\times \frac{2}{3}=.... \\ Vậy \frac{2}{3}\times \frac{4}{5}......\frac{4}{5}\times \frac{2}{3} \\ Nhận xét:(\frac{1}{3}\times \frac{2}{5})\times \frac{3}{4}=.... \\ \frac{1}{3}\times (\frac{2}{5}\times \frac{3}{4})=.... \\ (\frac{1}{3}\times \frac{2}{5})\times \frac{3}{4}....\frac{1}{3}\times (\frac{2}{5}\times \frac{3}{4}) \\ Nhận xét:(\frac{1}{5}\times \frac{2}{5})\times \frac{3}{4}=.... \\ \frac{1}{5}\times \frac{3}{4}+\frac{2}{5}\times \frac{3}{4}=.... \\ Vậy \left(\frac{1}{5}+\frac{2}{5}\right)\times \frac{3}{4}...\frac{1}{5}\times \frac{3}{4}+\frac{2}{5}\times \frac{3}{4} \end{gathered}$$