If A ∩ B = ∅, n(A) = p, and n(B) = q, what is n(A ∪ B)?
Answer and explanation
Correct answer: p + q
For any two finite sets, n(A ∪ B) = n(A) + n(B) − n(A ∩ B). Here A ∩ B is the empty set, so it has zero elements: n(A ∩ B) = 0. Substituting the given values gives n(A ∪ B) = p + q − 0 = p + q. Because the sets are disjoint, no common element is counted twice.
Frequently asked questions
What is the correct answer to this question?
p + q
Why is this the correct answer?
For any two finite sets, n(A ∪ B) = n(A) + n(B) − n(A ∩ B). Here A ∩ B is the empty set, so it has zero elements: n(A ∩ B) = 0. Substituting the given values gives n(A ∪ B) = p + q − 0 = p + q. Because the sets are disjoint, no common element is counted twice.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Operations on Sets (Union, Intersection, Difference).