If A = {x : x ∈ ℕ, x is a multiple of 9 and x < 50}, how many elements are in A?
Answer and explanation
Correct answer: 5
The positive multiples of 9 are 9, 18, 27, 36, 45, 54, and so on. The condition x < 50 allows the first five values but excludes 54 and every later multiple. Therefore A = {9, 18, 27, 36, 45}, which contains exactly 5 distinct elements. The strict inequality is important because 50 itself would not be included even if it were a multiple of 9.
Frequently asked questions
What is the correct answer to this question?
5
Why is this the correct answer?
The positive multiples of 9 are 9, 18, 27, 36, 45, 54, and so on. The condition x < 50 allows the first five values but excludes 54 and every later multiple. Therefore A = {9, 18, 27, 36, 45}, which contains exactly 5 distinct elements. The strict inequality is important because 50 itself would not be included even if it were a multiple of 9.
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.
