If A = {x ∈ N : 3 divides x, x ≤ 21} and B = {x ∈ N : 7 divides x, x ≤ 21}, what is A ∪ B?
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Answer and explanation
Correct answer: {3,6,7,9,12,14,15,18,21}
The multiples of 3 not exceeding 21 are A = {3,6,9,12,15,18,21}. The multiples of 7 not exceeding 21 are B = {7,14,21}. A union contains every distinct element from both sets, so A ∪ B = {3,6,7,9,12,14,15,18,21}. The common element 21 is listed only once.
Frequently asked questions
What is the correct answer to this question?
{3,6,7,9,12,14,15,18,21}
Why is this the correct answer?
The multiples of 3 not exceeding 21 are A = {3,6,9,12,15,18,21}. The multiples of 7 not exceeding 21 are B = {7,14,21}. A union contains every distinct element from both sets, so A ∪ B = {3,6,7,9,12,14,15,18,21}. The common element 21 is listed only once.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Operations on Sets (Union, Intersection, Difference).
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