What is the sum of the first (80) natural numbers?
Answer and explanation
Correct answer: 3240
The sum of the first \(n\) natural numbers is \(S_n=\frac{n(n+1)}{2}\). Therefore, \(S_{80}=\frac{80\times81}{2}=40\times81=3240\). Hence, option B is correct. The other values result from an error in multiplying 80 and 81 or dividing by 2. Exam tip: use \(\frac{n(n+1)}{2}\) for the sum of consecutive natural numbers starting from 1.
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 \(S_n=\frac{n(n+1)}{2}\). Therefore, \(S_{80}=\frac{80\times81}{2}=40\times81=3240\). Hence, option B is correct. The other values result from an error in multiplying 80 and 81 or dividing by 2. Exam tip: use \(\frac{n(n+1)}{2}\) for the sum of consecutive natural numbers starting from 1.
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.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
