Tham khảo
`a) \frac{2}{3}.\frac{4}{9}+\frac{2}{3}.\frac{5}{9}`
`=\frac{2}{3}.(\frac{4}{9}+\frac{5}{9})`
`=\frac{2}{3}.1=\frac{2}{3}`
`b) \frac{2}{5}:\frac{3}{7}.\frac{3}{7}:\frac{2}{5}+2019`
`=\frac{2}{5}:\frac{2}{5}+2019`
`=1+2019=2020`
`\text{©CBT}`