Which sum is formed when (20) is added to (1+2+3+\cdots+19)?
Answer and explanation
Correct answer: \(S_{20}\)
Here, \(S_n\) denotes the sum of the first \(n\) natural numbers. Adding 20 to \(1+2+3+\cdots+19\) gives \(1+2+3+\cdots+19+20\), which is \(S_{20}\). \(S_{19}\) includes terms only up to 19, so it is not correct. Exam tip: use the last included natural number to identify the subscript of the sum.
Frequently asked questions
What is the correct answer to this question?
\(S_{20}\)
Why is this the correct answer?
Here, \(S_n\) denotes the sum of the first \(n\) natural numbers. Adding 20 to \(1+2+3+\cdots+19\) gives \(1+2+3+\cdots+19+20\), which is \(S_{20}\). \(S_{19}\) includes terms only up to 19, so it is not correct. Exam tip: use the last included natural number to identify the subscript of the sum.
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.
