How much greater is the sum of the first (40) natural numbers than the sum of the first (20) natural numbers?
Answer and explanation
Correct answer: 610
The sum of the first 40 natural numbers is \(S_{40}=\frac{40\times41}{2}=820\), and the sum of the first 20 natural numbers is \(S_{20}=\frac{20\times21}{2}=210\). Therefore, the required difference is \(820-210=610\), so option C is correct. Getting 600 usually results from an arithmetic error in multiplication or subtraction. Exam tip: In such questions, use \(S_n=\frac{n(n+1)}{2}\) and subtract the two sums.
Frequently asked questions
What is the correct answer to this question?
610
Why is this the correct answer?
The sum of the first 40 natural numbers is \(S_{40}=\frac{40\times41}{2}=820\), and the sum of the first 20 natural numbers is \(S_{20}=\frac{20\times21}{2}=210\). Therefore, the required difference is \(820-210=610\), so option C is correct. Getting 600 usually results from an arithmetic error in multiplication or subtraction. Exam tip: In such questions, use \(S_n=\frac{n(n+1)}{2}\) and subtract the two sums.
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.
