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# If the sum of the first n positive integers is S, what is

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Director
Joined: 06 Feb 2006
Posts: 893

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If the sum of the first n positive integers is S, what is [#permalink]

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24 Oct 2006, 10:29
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If the sum of the first n positive integers is S, what is the sum of the first n positive even integers, in terms of S ?

(A) S/2
(B) S
(C) 2S
(D) 2S + 2
(E) 4S

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Director
Joined: 13 Nov 2003
Posts: 788

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Location: BULGARIA

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24 Oct 2006, 10:53
The sum of first 5 inegers is 15. Sum of first five even integers is 30 or 2S so C)

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Director
Joined: 06 Feb 2006
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24 Oct 2006, 10:54
BG wrote:
The sum of first 5 inegers is 15. Sum of first five even integers is 30 or 2S so C)

Totaly misinterpereted the question.... did the same stuff with picking numbers, but the question was asking for the different thing

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Senior Manager
Joined: 05 Oct 2006
Posts: 266

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25 Oct 2006, 01:49
choice c

sum of 1st n numbers = n/2(n+1) = s

sum of 1st n even nos = n/2(1st term+last term) = n/2(2+last term)
where last term = 2 + (n-1)*2, 2 is the common difference

hence sum of 1st n even nos = n/2(4+(n-1)*2)=n(n+1) = 2 S

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VP
Joined: 15 Jul 2004
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Schools: Wharton (R2 - submitted); HBS (R2 - submitted); IIMA (admitted for 1 year PGPX)

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25 Oct 2006, 02:14
SimaQ wrote:
BG wrote:
The sum of first 5 inegers is 15. Sum of first five even integers is 30 or 2S so C)

Totaly misinterpereted the question.... did the same stuff with picking numbers, but the question was asking for the different thing

What misinterpretation I don't understand. I think the answer is 2S

Kudos [?]: 218 [0], given: 13

Director
Joined: 06 Feb 2006
Posts: 893

Kudos [?]: 123 [0], given: 0

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25 Oct 2006, 04:46
dwivedys wrote:
SimaQ wrote:
BG wrote:
The sum of first 5 inegers is 15. Sum of first five even integers is 30 or 2S so C)

Totaly misinterpereted the question.... did the same stuff with picking numbers, but the question was asking for the different thing

What misinterpretation I don't understand. I think the answer is 2S

No no, the answer is good... I missinterpreted the question.... Answer is 2S

Kudos [?]: 123 [0], given: 0

25 Oct 2006, 04:46
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