.........gup mình với

`a) 4/6 + 7/13 + 17/9 + 19/13 + 1/9 + 14/16`

`= ( 7/13 + 19/13 ) + ( 17/9 + 1/9 ) + 4/6 + 14/16`

`= 2 + 2 + 2/3 + 7/8`

`= 48/24 + 48/24 + 16/24 + 21/24`

`= (48+48+16+21)/24`

`= 133/24`

`b) 23/14 xx 6/13 - 9/14 xx 6/13`

`= ( 23/14 - 9/14 ) xx 6/13`

`= 1 xx 6/13`

`= 6/13`