What is the roster form of D₁ = {x : x ∈ ℕ, the tens digit of x is 2, and x < 30}?
Answer and explanation
Correct answer: D₁ = {20, 21, 22, 23, 24, 25, 26, 27, 28, 29}
A number with tens digit 2 lies in the interval from 20 through 29. Every one of these numbers is a natural number and is less than 30, so all of them satisfy the defining conditions. Therefore, the roster form contains every integer from 20 to 29 exactly once. The restriction is about the tens digit, not the units digit, so odd and even numbers are both included.
Frequently asked questions
What is the correct answer to this question?
D₁ = {20, 21, 22, 23, 24, 25, 26, 27, 28, 29}
Why is this the correct answer?
A number with tens digit 2 lies in the interval from 20 through 29. Every one of these numbers is a natural number and is less than 30, so all of them satisfy the defining conditions. Therefore, the roster form contains every integer from 20 to 29 exactly once. The restriction is about the tens digit, not the units digit, so odd and even numbers are both included.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Sets and their representations.
