What is the value of (1+2+3+\cdots+80)?
Answer and explanation
Correct answer: 3240
The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Therefore, \(1+2+\cdots+80=\frac{80\times81}{2}=40\times81=3240\). Hence, option C is correct. A value such as 3230 can result from an arithmetic error while halving or multiplying. Exam tip: For the sum of consecutive natural numbers, use \(\frac{n(n+1)}{2}\).
Frequently asked questions
What is the correct answer to this question?
3240
Why is this the correct answer?
The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Therefore, \(1+2+\cdots+80=\frac{80\times81}{2}=40\times81=3240\). Hence, option C is correct. A value such as 3230 can result from an arithmetic error while halving or multiplying. Exam tip: For the sum of consecutive natural numbers, use \(\frac{n(n+1)}{2}\).
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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