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Class 9 Mathematics Sequences and Progressions Sum of first n natural numbersHard

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If (S_n-S_{n-1}=84), what will be (S_{n-1})?

Answer and explanation

Correct answer: (3486)

(S_n-S_{n-1}=n), so (n=84) and (S_{83}=\frac{83\cdot84}{2}=3486). For the previous sum, take (n-1).

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Sequences Progressions Natural-Numbers Previous-Sum Sum Of First N Natural Numbers Sequences And Progressions Mathematics Class 9 Mcq

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