Let U = {1, 2, ..., 20}, A = {x ∈ U : x is prime}, and B = {x ∈ U : x is odd}. What is A \ B?
Answer and explanation
Correct answer: {2}
The primes in U are {2, 3, 5, 7, 11, 13, 17, 19}. The difference A \ B keeps primes that are not odd. Every prime other than 2 is odd, so 3, 5, 7, 11, 13, 17, and 19 are removed. The number 2 is prime and even, hence it remains. Therefore A \ B = {2}, making option A correct; 1 is not prime, so option D is also incorrect.
Frequently asked questions
What is the correct answer to this question?
{2}
Why is this the correct answer?
The primes in U are {2, 3, 5, 7, 11, 13, 17, 19}. The difference A \ B keeps primes that are not odd. Every prime other than 2 is odd, so 3, 5, 7, 11, 13, 17, and 19 are removed. The number 2 is prime and even, hence it remains. Therefore A \ B = {2}, making option A correct; 1 is not prime, so option D is also incorrect.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Operations on Sets (Union, Intersection, Difference).
