Question
If n(∪)=700, n(A)=200, n(B)=300 and n(A∩B)=100, then n(A′∩B′)= ___.
Answer: Option C
:
C
From de-Morgan's law of complementation, we have A′∩B′=(A∪B)′.
⇒n(A′∩B′)=n((A∪B)′)
But,n((A∪B)′)=n(U)−n(A∪B) by definition of complement of a set.
∴n(A′∩B′)=n(U)−n(A∪B)
=n(U)−[n(A)+n(B)−n(A∩B)]
=700−(200+300−100)
=300
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:
C
From de-Morgan's law of complementation, we have A′∩B′=(A∪B)′.
⇒n(A′∩B′)=n((A∪B)′)
But,n((A∪B)′)=n(U)−n(A∪B) by definition of complement of a set.
∴n(A′∩B′)=n(U)−n(A∪B)
=n(U)−[n(A)+n(B)−n(A∩B)]
=700−(200+300−100)
=300
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