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What is the difference between the sums of the first (28) and first (14) natural numbers?

Answer and explanation

Correct answer: 301

The sum of the first n natural numbers is
\(S_n=\frac{n(n+1)}{2}\). Thus, \(S_{28}=\frac{28\times29}{2}=406\) and \(S_{14}=\frac{14\times15}{2}=105\). Therefore, the difference is \(406-105=301\). An answer such as 291 usually results from an arithmetic error while subtracting the sum up to 14. Exam tip: for a difference of sums, calculate both sums using the formula and subtract the smaller one from the larger one.

Related tags

Natural NumbersSum FormulaSequences And ProgressionsArithmetic SeriesClass 9 MathematicsSum Of First N Natural NumbersMathematicsClass 9 Mcq

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