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Let \(S_n=1+2+3+\cdots+n\). Which expression represents the sum of the last 8 consecutive natural numbers ending at \(n\)?

Answer and explanation

Correct answer: \(S_n-S_{n-8}\)

\(S_n\) contains the sum from 1 to \(n\). Subtracting \(S_{n-8}\) removes terms through \(n-8\), leaving \((n-7)+\cdots+n\), exactly 8 terms. \(S_{n+8}-S_n\) gives the next 8 terms instead. Exam tip: count the remaining terms.

Related tags

Natural NumbersSum FormulaSequences And ProgressionsConsecutive TermsAlgebraic ExpressionsSum Of First N Natural NumbersMathematicsClass 9 Mcq

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