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What is the difference between the sums of the first (180) and first (120) natural numbers?

Answer and explanation

Correct answer: 9030

The sum of the first n natural numbers is \(S_n=\frac{n(n+1)}{2}\). Thus, \(S_{180}=\frac{180\times181}{2}=16290\) and \(S_{120}=\frac{120\times121}{2}=7260\). Therefore, the difference is \(16290-7260=9030\). It is also the sum of the integers from \(121\) to \(180\). Exam tip: The difference of two such sums equals the sum of the terms lying between them.

Related tags

Sequences And ProgressionsNatural NumbersSum Of N TermsArithmetic SeriesNumber PatternsSum Of First N Natural NumbersMathematicsClass 9 Mcq

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