A student adds the first (18) natural numbers. What is the correct sum?
Answer and explanation
Correct answer: 171
The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Substituting \(n=18\) gives \(\frac{18\times19}{2}=171\), so option A is correct. \(190\) is the sum from \(1\) to \(19\), not from \(1\) to \(18\). Exam tip: in \(n(n+1)/2\), use \(n\) as the number of terms given in the question.
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 \(\frac{n(n+1)}{2}\). Substituting \(n=18\) gives \(\frac{18\times19}{2}=171\), so option A is correct. \(190\) is the sum from \(1\) to \(19\), not from \(1\) to \(18\). Exam tip: in \(n(n+1)/2\), use \(n\) as the number of terms given in the question.
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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