What is the number of elements in the set {x ∈ ℕ : 2x + 1 < 20}?
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Answer and explanation
Correct answer: 9
Solve the inequality: 2x + 1 < 20 gives 2x < 19, so x < 9.5. Since x belongs to the natural numbers and, in the usual school convention, ℕ = {1, 2, 3, ...}, the possible values are 1 through 9. Therefore, the set is {1, 2, 3, 4, 5, 6, 7, 8, 9} and has 9 elements. Hence, option B is correct.
Frequently asked questions
What is the correct answer to this question?
9
Why is this the correct answer?
Solve the inequality: 2x + 1 < 20 gives 2x < 19, so x < 9.5. Since x belongs to the natural numbers and, in the usual school convention, ℕ = {1, 2, 3, ...}, the possible values are 1 through 9. Therefore, the set is {1, 2, 3, 4, 5, 6, 7, 8, 9} and has 9 elements. Hence, option B is correct.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: The Empty Set, Finite and Infinite Sets, Equal Sets.
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