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If (S_n-S_{n-5}=390), what will be the value of (n)?
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Answer and explanation
Correct answer: (78)
The difference is ((n-4)+(n-3)+(n-2)+(n-1)+n=5n-10), so (5n-10=390) gives (n=80). Form the sum of the last five terms.
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What is the correct answer to this question?
(78)
Why is this the correct answer?
The difference is ((n-4)+(n-3)+(n-2)+(n-1)+n=5n-10), so (5n-10=390) gives (n=80). Form the sum of the last five terms.
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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