What is the difference between the sum of the first (26) natural numbers and (26)?
Answer and explanation
Correct answer: 325
The sum of the first 26 natural numbers is
\(S_{26}=\frac{26\times27}{2}=351\). Therefore, subtracting 26 gives
\(351-26=325\). This is also the sum of the first 25 natural numbers. For example, 315 is not the correct sum of the first 25 natural numbers. Exam tip: remember that the sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\).
Frequently asked questions
What is the correct answer to this question?
325
Why is this the correct answer?
The sum of the first 26 natural numbers is
\(S_{26}=\frac{26\times27}{2}=351\). Therefore, subtracting 26 gives
\(351-26=325\). This is also the sum of the first 25 natural numbers. For example, 315 is not the correct sum of the first 25 natural numbers. Exam tip: remember that the sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\).
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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