If n(A) = 18 and n(A ∩ B) = 7, what is n(A − B)?
Answer and explanation
Correct answer: 11
The set A is divided into two disjoint parts: the elements in A ∩ B and the elements in A − B. Therefore n(A) = n(A ∩ B) + n(A − B). Rearranging gives n(A − B) = 18 − 7 = 11. Hence option C is correct. The value 7 counts the common elements, while 18 counts all elements of A, so neither is the required difference.
Frequently asked questions
What is the correct answer to this question?
11
Why is this the correct answer?
The set A is divided into two disjoint parts: the elements in A ∩ B and the elements in A − B. Therefore n(A) = n(A ∩ B) + n(A − B). Rearranging gives n(A − B) = 18 − 7 = 11. Hence option C is correct. The value 7 counts the common elements, while 18 counts all elements of A, so neither is the required difference.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Operations on Sets (Union, Intersection, Difference).
