Đáp án:

 `4/9 + 5/54`

`= 24/54 + 5/54`

`= 29/54`

`----`

`11/9 - 5/8`

`= 88/72 - 45/72`

`= 43/72`

`----`

`1/20 + 2/3`

`= 3/60 + 40/60`

`= 43/60`

`----`

`1 - 4/2003`

`= 2003/2003 - 4/2003`

`= 1999/2003`

`----`

`1 : 3/7`

`= 1 xx 7/3`

`= 7/3`

`----`

`18/5 xx 15/6`

`= (18 xx 15)/(5xx6)`

`= (6xx3xx3xx5)/(5xx6)`

`= 9/1`

`= 9`

`----`

`7/19 : 21/38`

`= 7/19 xx 38/21`

`= (7xx38)/(19xx21)`

`= (7xx19xx2)/(19xx7xx3)`

`= 2/3`

`----`

`7 xx 3/34`

`= (7xx3)/34`

`= 21/34`