31/80+(3/16+39/80)=
2/45+(3/45+7/9)=
(3/7+5/14)+1/14=
7/15+(2/15+1/5)=
3/16+(1/16+5/8)=
(1/13+1/14)+12/13=

Надо расписать!
Дам 15 балов

1) 31/80 +54/80
85/80=17/16

31/80+(3/16+39/80)=31/80+(15/80+39/80)=31/80+54/80=85/80=1 5/80=1 1/16
2/45+(3/45+7/9)=2/45+(3/45+35/45)=2/45+38/45=4045=8/9
(3/7+5/14)+1/14=(6/14+5/14)+1/14=11/14+1/14=12/14=6/7
7/15+(2/15+1/5)=7/15+(2/15+3/15)=7/15+5/15=12/15=4/5
3/16+(1/16+5/8)=3/16+(1/16+10/16)=3/16+11/16=14/16=7/8
(1/13+1/14)+12/13=(14/182+13/182)+