Đáp án+Giải thích các bước giải:
`8/11` × `7/4` - `8/11` × `3/8`
= `8/11` × `(7/4 - 3/8)`
= `8/11` × `11/8`
= `1`
`15/13` × `54/20` - `15/13` × `1/10`
= `15/13` × `(54/20 - 1/10)`
= `15/13` × `13/5`
= `3`
`8/9` × `3/7` × `8/5` × `1/4`
= `(8×3×8×1)/(9×7×5×4)`
= `192/1260`
= `16/105`
`5/6` : `7` + `20/21` : `7` + `5/6` : `7`
= `5/6` × `1/7` + `20/21` × `1/7` + `5/6` × `1/7`
= `1/7` × `(5/6 + 20/21 + 5/6)`
= `1/7` × `55/21`
= `55/147`
