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GATE 2020 CH – Question 5

General Aptitude · Quantitative Aptitude: Algebra, Geometry and Mensuration · 1 mark · Multiple choice

Find the difference between the sum of the first 2n natural numbers and the sum of the first n odd natural numbers.

  1. $n^2-n$
  2. $n^2+n$
  3. $2n^2-n$
  4. $2n^2+n$

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Correct answer: (B) $n^2+n$

Explanation

The first sum is $(2n)(2n+1)/2=n(2n+1)$. The sum of the first n odd numbers is $n^2$. Subtracting gives $2n^2+n-n^2=n^2+n$, option B.

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