a) card(A intersectat B)=card(A)+card(B)-card(A reunit B)
card(A intersectat B)=5+7-10
card (A intersectat B)=12-10
card (A intersectat B)=2
b) card(A intersectat B)=card(A)-card(A\B)
card(A intersectat B)=10-4
card(A intersectat B)=6
c) card(A intersectat B)=card(B)