If the sum of the first (n) natural numbers is (36), what is (n)?
Answer and explanation
Correct answer: 8
The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Thus, \(\frac{n(n+1)}{2}=36\). On substituting \(n=8\), we get \(\frac{8\times9}{2}=36\), so 8 is correct. For \(n=7\), the sum is only \(28\). Exam tip: for small answer choices, substitute each value in \(n(n+1)/2\) to check quickly.
Frequently asked questions
What is the correct answer to this question?
8
Why is this the correct answer?
The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Thus, \(\frac{n(n+1)}{2}=36\). On substituting \(n=8\), we get \(\frac{8\times9}{2}=36\), so 8 is correct. For \(n=7\), the sum is only \(28\). Exam tip: for small answer choices, substitute each value in \(n(n+1)/2\) to check quickly.
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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