If S={x:x∈N, x is a factor of 18 or x=12}, what is n(S)?
Answer and explanation
Correct answer: 7
The governing concept is the cardinality of a union of set conditions. The positive factors of 18 are 1, 2, 3, 6, 9, and 18. The second condition adds 12, which is not already present. Therefore S={1,2,3,6,9,12,18}, so it has 7 distinct elements. A repeated element would be counted only once in a set, making option C correct.
Frequently asked questions
What is the correct answer to this question?
7
Why is this the correct answer?
The governing concept is the cardinality of a union of set conditions. The positive factors of 18 are 1, 2, 3, 6, 9, and 18. The second condition adds 12, which is not already present. Therefore S={1,2,3,6,9,12,18}, so it has 7 distinct elements. A repeated element would be counted only once in a set, making option C correct.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Number Systems.
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