Verified answer

3.

а)7/11+2/11=9/11

б)12+3/7=12 3/7

в)6/13-2/13=4/13

г)(3/7+4/7)+(7/10-3/10)=7/7+4/10=1+2/5=1 2/5

4.

а)5 3/8+3 4/8=(5+3)+(3/8+4/8)=8 7/8

б)8 16/19-7 14/19=(8-7)+(16/19-14/19)=1 2/19

в)8 13/20-7=(8-7)+13/20=1 13/20

г)7-5 5/6=6 6/6-5 5/6=(6-5)+(6/6-5/6)=1 1/6