How many elements are in A = {x : x is a square number less than 20}?
Answer and explanation
Correct answer: 4
Taking square numbers as positive natural-number squares, list the squares below 20: 1² = 1, 2² = 4, 3² = 9, and 4² = 16. The next square is 5² = 25, which is not less than 20. Therefore A = {1, 4, 9, 16}, containing four distinct elements. It is finite, so option B is correct; 3 misses one square, 5 includes an excluded value, and the set is not infinite.
Frequently asked questions
What is the correct answer to this question?
4
Why is this the correct answer?
Taking square numbers as positive natural-number squares, list the squares below 20: 1² = 1, 2² = 4, 3² = 9, and 4² = 16. The next square is 5² = 25, which is not less than 20. Therefore A = {1, 4, 9, 16}, containing four distinct elements. It is finite, so option B is correct; 3 misses one square, 5 includes an excluded value, and the set is not infinite.
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.
