a)20/3-21/9(simplifici 21/9 cu 3)=20/3-7/3=13/3;
b)21/5-27/15(simplifici 27/15 cu 3)=21/5-9/5=12/5;
c)30/7-36/42(simplifici 36/42 cu 6)=30/7-6/7=24/7;
d)41/6-35/30(simplifici 35/30 cu 5)=41/6-7/6=34/6;
e)31/8-15/40(simplifici 15/40 cu 5)=31/8-3/8=28/3;
f)25/9-28/63(simplifici 28/63 cu 7)=25/9-4/9=21/9.
