а)

5 5/9+2 1/9 +1 2/9=

=(5+2+1)+(5/9+1/9+2/9)=

=8 8/9

б)

8 5/11 -3 8/11 +4 9/11=

=(8-3+4)+(5/11-8/11+9/11)=

=9 6/11

в)

7 1/3 +4 1/3 +2/3=

=(7+4)+(1/3+1/3+2/3)=

=11 4/3=12 1/3

г)

5 11/21 +4 5/21 -6 7/21=

=(5+4-6)+(11/21+5/21-7/21)=

=3 9/21=3 3/7

д)

8 3/8 +5 5/8 -2 7/8=

=(8+5-2)+(3/8+5/8-7/8)=

=11 1/8