1/5+3/7=28/35+15/35=43/35=1 8/35
5/12+9/20=25/60+27/60=52/60=13/15
5/18+4/45=25/90+8/90=33/90=11/30
12/17+27/34=24/34+27/34=51/34=1 17/34= 1 1/2=1,5
5/9-7/18=10/18-7/18=3/18=1/6
4/5-5/8=32/40-25/40=7/40
11/16-5/12=33/48-20/48=13/48
8/21-4/35=40/105-12/105=28/105