Let U = {1, 2, ..., 20}, A be the set of prime numbers in U, and B be the set of odd numbers in U. What is A − B?
Answer and explanation
Correct answer: {2}
The governing concept is set difference: A − B consists of elements that belong to A but do not belong to B. The primes from 1 through 20 are 2, 3, 5, 7, 11, 13, 17, and 19. All primes except 2 are odd and therefore lie in B. Since 2 is even, it is the only prime excluded from B, giving A − B = {2}. Thus option A is correct; option C is A’s odd-prime part, not the difference.
Frequently asked questions
What is the correct answer to this question?
{2}
Why is this the correct answer?
The governing concept is set difference: A − B consists of elements that belong to A but do not belong to B. The primes from 1 through 20 are 2, 3, 5, 7, 11, 13, 17, and 19. All primes except 2 are odd and therefore lie in B. Since 2 is even, it is the only prime excluded from B, giving A − B = {2}. Thus option A is correct; option C is A’s odd-prime part, not the difference.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Operations on Sets (Union, Intersection, Difference).
