3/8+5/9+5/8+4/9=(3/8+5/8)+(5/9+4/9)=8/8+9/9=1+1=2
4/15+3/7+11/15+6/7=(4/15+11/15)+(3/7+6/7)=15/15+9/7=1+1 2/7=2 2/7
8 11/24-5,35 =8,458-5,35=3,108
6,625-3 6/17=6,625-3,353=3,272
