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PS: Positive Integer

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SVP
SVP
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Joined: 29 Aug 2007
Posts: 2473

Kudos [?]: 832 [0], given: 19

PS: Positive Integer [#permalink]

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New post 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)
_________________

Verbal: http://gmatclub.com/forum/new-to-the-verbal-forum-please-read-this-first-77546.html
Math: http://gmatclub.com/forum/new-to-the-math-forum-please-read-this-first-77764.html
Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html


GT

Kudos [?]: 832 [0], given: 19

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Joined: 21 Apr 2008
Posts: 269

Kudos [?]: 162 [0], given: 0

Location: Motortown
Re: PS: Positive Integer [#permalink]

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New post 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)

Kudos [?]: 162 [0], given: 0

Senior Manager
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Joined: 30 Nov 2008
Posts: 485

Kudos [?]: 349 [0], given: 15

Schools: Fuqua
Re: PS: Positive Integer [#permalink]

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New post 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 :oops: 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) :oops:

Kudos [?]: 349 [0], given: 15

SVP
SVP
User avatar
Joined: 29 Aug 2007
Posts: 2473

Kudos [?]: 832 [0], given: 19

Re: PS: Positive Integer [#permalink]

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New post 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)
_________________

Verbal: http://gmatclub.com/forum/new-to-the-verbal-forum-please-read-this-first-77546.html
Math: http://gmatclub.com/forum/new-to-the-math-forum-please-read-this-first-77764.html
Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html


GT

Kudos [?]: 832 [0], given: 19

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

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