If R₁ = {x : x is a two-digit prime number and x < 20}, which is the roster form of R₁?
Answer and explanation
Correct answer: R₁ = {11, 13, 17, 19}
A two-digit number is at least 10, and the condition x < 20 restricts the search to 10 through 19. Among these numbers, 11, 13, 17, and 19 have no positive divisors other than 1 and themselves, so they are prime. The other candidates are composite: 10, 12, 14, 15, 16, and 18. Therefore option A gives the correct roster form.
Frequently asked questions
What is the correct answer to this question?
R₁ = {11, 13, 17, 19}
Why is this the correct answer?
A two-digit number is at least 10, and the condition x < 20 restricts the search to 10 through 19. Among these numbers, 11, 13, 17, and 19 have no positive divisors other than 1 and themselves, so they are prime. The other candidates are composite: 10, 12, 14, 15, 16, and 18. Therefore option A gives the correct roster form.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Sets and their representations.
