Let U={x∈N: 1≤x≤18}, A={x: x is divisible by 3}, and B={x: x is even}. How many elements are in Aᶜ∩Bᶜ?
Answer and explanation
Correct answer: 6
Aᶜ∩Bᶜ contains numbers from 1 through 18 that are neither divisible by 3 nor even. The odd numbers in this range are 1,3,5,7,9,11,13,15,17. Removing the odd multiples of 3, namely 3,9, and 15, leaves {1,5,7,11,13,17}. Thus the set has 6 elements. Equivalently, De Morgan’s law gives Aᶜ∩Bᶜ=(A∪B)ᶜ.
Frequently asked questions
What is the correct answer to this question?
6
Why is this the correct answer?
Aᶜ∩Bᶜ contains numbers from 1 through 18 that are neither divisible by 3 nor even. The odd numbers in this range are 1,3,5,7,9,11,13,15,17. Removing the odd multiples of 3, namely 3,9, and 15, leaves {1,5,7,11,13,17}. Thus the set has 6 elements. Equivalently, De Morgan’s law gives Aᶜ∩Bᶜ=(A∪B)ᶜ.
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.