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Find the value of (S_{35}-S_{19}).

Answer and explanation

Correct answer: 440

The sum of the first n natural numbers is \(S_n=\frac{n(n+1)}{2}\). Thus, \(S_{35}=\frac{35\times36}{2}=630\) and \(S_{19}=\frac{19\times20}{2}=190\). Therefore, \(S_{35}-S_{19}=630-190=440\). It is also the sum of the natural numbers from 20 to 35. Exam tip: \(S_b-S_a\) represents the sum from \(a+1\) to \(b\).

Related tags

Sequences And ProgressionsNatural NumbersSum Of N Natural NumbersArithmetic SeriesClass 9 MathematicsSum Of First N Natural NumbersMathematicsClass 9 Mcq

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