Which is the sum of the first (18) natural numbers?
Answer and explanation
Correct answer: 171
The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Here, \(n=18\), so \(\frac{18\times19}{2}=9\times19=171\). Therefore, 171 is the correct answer. The value 180 may result from using \(18\times10\), but the correct formula uses \(n+1=19\). Exam tip: Write \(n(n+1)/2\) and divide the even factor by 2 first.
Frequently asked questions
What is the correct answer to this question?
171
Why is this the correct answer?
The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Here, \(n=18\), so \(\frac{18\times19}{2}=9\times19=171\). Therefore, 171 is the correct answer. The value 180 may result from using \(18\times10\), but the correct formula uses \(n+1=19\). Exam tip: Write \(n(n+1)/2\) and divide the even factor by 2 first.
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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