If U = {p,q,r,s,t}, A = {p,q,r}, and B = {r,s}, what is (A ∩ B)′?
Answer and explanation
Correct answer: {p,q,s,t}
First find the intersection. The only element common to A = {p,q,r} and B = {r,s} is r, so A ∩ B = {r}. The complement is taken in U, not in an unrestricted universe. Removing r from U = {p,q,r,s,t} leaves {p,q,s,t}. Hence (A ∩ B)′ = {p,q,s,t}, so option B is correct.
Frequently asked questions
What is the correct answer to this question?
{p,q,s,t}
Why is this the correct answer?
First find the intersection. The only element common to A = {p,q,r} and B = {r,s} is r, so A ∩ B = {r}. The complement is taken in U, not in an unrestricted universe. Removing r from U = {p,q,r,s,t} leaves {p,q,s,t}. Hence (A ∩ B)′ = {p,q,s,t}, so option B is correct.
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.