Find the sum of the first (39) natural numbers.
Answer and explanation
Correct answer: 780
The sum of the first \(n\) natural numbers is \(S_n=\frac{n(n+1)}{2}\). Therefore, \(S_{39}=\frac{39\times40}{2}=39\times20=780\). Option 760 equals \(38\times20\), so it is not the sum of the first 39 natural numbers. Exam tip: For the sum from \(1\) to \(n\), use \(n(n+1)/2\).
Frequently asked questions
What is the correct answer to this question?
780
Why is this the correct answer?
The sum of the first \(n\) natural numbers is \(S_n=\frac{n(n+1)}{2}\). Therefore, \(S_{39}=\frac{39\times40}{2}=39\times20=780\). Option 760 equals \(38\times20\), so it is not the sum of the first 39 natural numbers. Exam tip: For the sum from \(1\) to \(n\), use \(n(n+1)/2\).
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.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
