50.
а)3/4-1/5=15-4/20=11/20
б)2/3-4/7=14-12/21=2/21
в)1/11+1/2=2+11/22=13/22
г)1/2+8/13=13+16/26=29/26=1 3/26
52.
а)3/7+0,4=3/7+4/10=30+28/70=58/70=29/35
б)6/11-0,3=6/11-3/10=60-33/110=27/110
в)0,8-5/6=8/10-5/6=24-25/30=-1/30
г)0,6+2/9=6/10+2/9=54+20/90=74/90=37/45