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If \(S_n=\frac{n(n+1)}{2}\), what is \(S_6\)?
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Answer and explanation
Correct answer: 21
Substitute \(n=6\) in the given formula: \(S_6=\frac{6(6+1)}{2}=\frac{6\times7}{2}=21\). Therefore, 21 is correct. A value such as 18 may result from substituting incorrectly. Exam tip: first find \(n+1\), then multiply and divide by 2.
Frequently asked questions
What is the correct answer to this question?
21
Why is this the correct answer?
Substitute \(n=6\) in the given formula: \(S_6=\frac{6(6+1)}{2}=\frac{6\times7}{2}=21\). Therefore, 21 is correct. A value such as 18 may result from substituting incorrectly. Exam tip: first find \(n+1\), then multiply and divide by 2.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Sum of first n natural numbers.
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