If U = {x : x ∈ ℕ, x ≤ 20} and A is the set of positive divisors of 20, what is n(A′)?
Answer and explanation
Correct answer: 14
Taking ℕ as the positive natural numbers, U = {1,2,...,20}, so n(U) = 20. The positive divisors of 20 are 1, 2, 4, 5, 10, and 20, giving n(A) = 6. The complement A′ contains the members of U that are not divisors of 20. Hence n(A′) = 20 − 6 = 14, so option C is correct.
Frequently asked questions
What is the correct answer to this question?
14
Why is this the correct answer?
Taking ℕ as the positive natural numbers, U = {1,2,...,20}, so n(U) = 20. The positive divisors of 20 are 1, 2, 4, 5, 10, and 20, giving n(A) = 6. The complement A′ contains the members of U that are not divisors of 20. Hence n(A′) = 20 − 6 = 14, so option C 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.