If A ⊆ B for sets A and B in a universal set U, which statement about their complements is correct?
Answer and explanation
Correct answer: B′ ⊆ A′
If A ⊆ B, every element of A is also in B. Consider an element of B′: it is not in B. Since every element of A would have to be in B, that element cannot be in A either; therefore it belongs to A′. Thus every element of B′ is in A′, giving B′ ⊆ A′. Taking complements reverses the direction of inclusion.
Frequently asked questions
What is the correct answer to this question?
B′ ⊆ A′
Why is this the correct answer?
If A ⊆ B, every element of A is also in B. Consider an element of B′: it is not in B. Since every element of A would have to be in B, that element cannot be in A either; therefore it belongs to A′. Thus every element of B′ is in A′, giving B′ ⊆ A′. Taking complements reverses the direction of inclusion.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Complement of a Set and Its Properties.