`\color{#1AD5F7}{⋆⟡}\color{#1AD5F7}{A}\color{#4DA6E6}{l}\color{#668EDD}{i}\color{#8077D5}{e}\color{#995FCD}{0}\color{#CC2FBC}{2}\color{#EA2F90}{⟡⋆}` 

Bài `9`

`a,4/21:8/15`

`=4/21xx15/8`

`=5/14`

`b,1/4:5/12`

`=1/4xx12/5`

`=3/5`

`c,5/7:10/21`

`=5/7xx21/10`

`=3/2`

`d,2/9:4/27`

`=2/9xx27/4`

`=3/2`