a) `-10/13` + `5/17` - `3/13` + `12/17` - `11/20`
= ( `-10/13` - `3/13`) + ( `5/17` + `12/17`) - `11/20`
= `-13/13` + `17/17` - `11/20`
= (-1) + 1 - `11/20`
= 0 - `11/20`
= `-11/20`
b) `3/4` + `-5/6` - `11/-12`
= `9/12` + `-10/12` - `-11/12`
= `-1/12` - `-11/12`
= `10/12`
= `5/6`
c) ( 13`4/9` + 2`1/9` ) - 3`4/9`
= `121/9` + `19/9` - `31/9`
= `140/9` - `31/9`
=`109/9`
d) `1,25` : `15/20` + ( 25% - `5/6` ) : 4`2/3`
= `5/4` : `3/4` + ( `1/4` - `5/6`) : `14/3`
= `5/3` + `-7/12` : `14/3`
= `5/3` + `-7/12` . `3/14`
= `5/3` + `1/8`
= `40/24` + `3/14`
= `43/24`