`4/15 . 1/3 . 15/20`

`=(4/15 . 15/20).1/3`

`=1/5 . 1/3`

`=1/15`

``

`2/3+20%.10/7`

`=2/3+1/4 . 10/7`

`=2/3 + 5/14`

`=43/42`

``

`6/21 - (-12)/44 + 10/14 - 1/(-4) - 18/33`

`=2/7 + 3/11 + 5/7 + 1/4 - 6/11`

`=(2/7 + 5/7) + (3/11 - 6/11) + 1/4`

`=1 - 3/11 + 1/4`

`=8/11 + 1/4`

`=43/44`

``

`(67/111 + 2/33 - 15/117).(1/3 - 25% - 1/12)`

`=(67/111 + 2/33 - 15/117).(1/3 - 1/4 - 1/12)`

`=(67/111 + 2/33 - 15/117).0`

`=0`