If (S_n=1176), what will be (S_{n-1})?
Answer and explanation
Correct answer: 1128
The sum of the first n natural numbers is \(S_n=\frac{n(n+1)}{2}\). Here, \(1176=\frac{48\times49}{2}\), so \(n=48\). Therefore, \(S_{n-1}=S_{47}=\frac{47\times48}{2}=1128\). The value 1176 is \(S_{48}\), not the sum up to the previous term. Exam tip: identify the given sum as half the product of two consecutive numbers first.
Frequently asked questions
What is the correct answer to this question?
1128
Why is this the correct answer?
The sum of the first n natural numbers is \(S_n=\frac{n(n+1)}{2}\). Here, \(1176=\frac{48\times49}{2}\), so \(n=48\). Therefore, \(S_{n-1}=S_{47}=\frac{47\times48}{2}=1128\). The value 1176 is \(S_{48}\), not the sum up to the previous term. Exam tip: identify the given sum as half the product of two consecutive numbers first.
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.
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