What will be the sum of the first (65) natural numbers?
Answer and explanation
Correct answer: 2145
The sum of the first \(n\) natural numbers is \(S_n=\frac{n(n+1)}{2}\). Therefore, \(S_{65}=\frac{65\times66}{2}=65\times33=2145\). Hence, 2145 is correct. A common mistake is to calculate \(65\times66\) but forget to divide by 2. Exam tip: for the sum of consecutive natural numbers from 1 to \(n\), use \(\frac{n(n+1)}{2}\).
Frequently asked questions
What is the correct answer to this question?
2145
Why is this the correct answer?
The sum of the first \(n\) natural numbers is \(S_n=\frac{n(n+1)}{2}\). Therefore, \(S_{65}=\frac{65\times66}{2}=65\times33=2145\). Hence, 2145 is correct. A common mistake is to calculate \(65\times66\) but forget to divide by 2. Exam tip: for the sum of consecutive natural numbers from 1 to \(n\), 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.
