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

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Director
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If the sum of the first n positive integers is S, what is [#permalink] New post 24 Oct 2006, 09:29
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


:)
Director
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 [#permalink] New post 24 Oct 2006, 09:53
The sum of first 5 inegers is 15. Sum of first five even integers is 30 or 2S so C)
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 [#permalink] New post 24 Oct 2006, 09:54
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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Re: Super hard Q [#permalink] New post 25 Oct 2006, 00:49
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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 [#permalink] New post 25 Oct 2006, 01:14
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
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 [#permalink] New post 25 Oct 2006, 03:46
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
  [#permalink] 25 Oct 2006, 03:46
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