If Y = {x : x ∈ N, x is prime, x + 2 is also prime, and x < 20}, what is Y?
Advertisement
Answer and explanation
Correct answer: Y = {3, 5, 11, 17}
The primes less than 20 are 2, 3, 5, 7, 11, 13, 17, and 19. Test the additional condition that x + 2 must also be prime: 3 gives 5, 5 gives 7, 11 gives 13, and 17 gives 19. The other candidates fail this condition, so Y = {3, 5, 11, 17}, making option A correct.
Frequently asked questions
What is the correct answer to this question?
Y = {3, 5, 11, 17}
Why is this the correct answer?
The primes less than 20 are 2, 3, 5, 7, 11, 13, 17, and 19. Test the additional condition that x + 2 must also be prime: 3 gives 5, 5 gives 7, 11 gives 13, and 17 gives 19. The other candidates fail this condition, so Y = {3, 5, 11, 17}, making option A correct.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Sets and their representations.
Advertisement