Salut!
a) 1/12 x 1/2 + 1/12 x 1/3 + 1/12 x 13/6=
1/12(1/2+1/3+13/6)=
1/12(3/6+2/6+13/6)=
1/12 x 18/6=
=3/12
=1/4
b) 1/8x5/6-4/9x1/8+1/8x1/18=
1/8(5/6-4/9+1/18)=
1/8(15/18-8/18+1/18)=
1/8x8/18=
=1/18
c) 2/12 x 61/13x6 +12/13=(e prea ciudat la punctul c..., si nici nu e factor comun)
1/6 x 61/78 +12/13=
61/13+12/13=
=73/13
Succes!