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# PS: Positive Integer

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SVP
Joined: 29 Aug 2007
Posts: 2452

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11 Dec 2008, 15:35
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If n is a positive integer, the sum of the integers from 1 to n, inclusive, equals (n(n+1))/2. Which of the following equals the sum of the integers from 1 to 2n, inclusive?

A. n(n+1)
B. (n(2n+1))/2
C. n(2n+1)
D. 2n(n+1)
E. 2n(2n+1)

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Senior Manager
Joined: 21 Apr 2008
Posts: 265
Location: Motortown

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11 Dec 2008, 17:04
GMAT TIGER wrote:
If n is a positive integer, the sum of the integers from 1 to n, inclusive, equals (n(n+1))/2. Which of the following equals the sum of the integers from 1 to 2n, inclusive?

A. n(n+1)
B. (n(2n+1))/2
C. n(2n+1)
D. 2n(n+1)
E. 2n(2n+1)

Is this some kind of trick question

C : n(2n+1)
Senior Manager
Joined: 30 Nov 2008
Posts: 482
Schools: Fuqua

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12 Dec 2008, 14:33
Yes. I agree with C.

The trick is some times to misguide us in solving the problem while sometimes it is straight forward applying the trivial fourmula. In fact I tried solving it, overlooking the fact that it is as simple as Sum of AP series = no of terms/2(first term + last term)

So it becomes 2n/2(1+2n) = n(1 + 2n)
SVP
Joined: 29 Aug 2007
Posts: 2452

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12 Dec 2008, 15:48
GMAT TIGER wrote:
If n is a positive integer, the sum of the integers from 1 to n, inclusive, equals (n(n+1))/2. Which of the following equals the sum of the integers from 1 to 2n, inclusive?

A. n(n+1)
B. (n(2n+1))/2
C. n(2n+1)
D. 2n(n+1)
E. 2n(2n+1)

OA is C.
sum of integers from 1 to n = n (n + 1)/2
sum of integers from 1 to 2n = 2n (2n + 1)/2 = n (2n + 1)

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

_________________

Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

GT

Re: PS: Positive Integer   [#permalink] 12 Dec 2008, 15:48
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