Given n(U)=20,n(A)=12,n(B)=9,n(A∩B)=4, where ∪ is the universal set, A and B are subset of ∪, then n(A∪Bc)=
17
9
11
3
16
Explanations for the correct option (4).
Expression of universal set A and B.
n(A∪B)=n(A)+n(B)-n(A∩B)
Substitute the values.
nA∪B=12+9-4=17
write the expression of n(A∪Bc)
n(A∪Bc)=n∪-nA∩B=20-17=3
Therefore, the correct option is (D).
If A and B are subsets of the universal set U, then show that,
A⊂B⇔A∪B=B