Answer: 6.
- A 3
- B 6
- C 9
- D 18
Correct answer: B. 6
Explanation: Since A ⊆ B, A ∪ B = B, so n(A ∪ B) = 6.
A Venn diagram makes set identities visual: A∪B is everything inside either circle, A∩B is only the overlap, and the region outside both circles represents the complement of their union - directly illustrating De Morgan's law (A∪B)′ = A′∩B′.
Concept context
Types of sets, operations (union/intersection/complement), relations, and types of functions with domain and range