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

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Director
Joined: 20 Sep 2006
Posts: 653
If the sum of the first n positive integers is S, what is [#permalink]

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07 Sep 2008, 19:38
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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
Intern
Joined: 26 Jan 2008
Posts: 26

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07 Sep 2008, 19:44
IMO C?

I don't think I did it the right way but i just ended up trying some numbers out

1+2+3+4 = 10
2+4+6+8 = 20

2+3+4+5+6 =20
2+4+6+8+10 = 30

whats the OA and what is another way to solve? thanks
Senior Manager
Joined: 09 Oct 2007
Posts: 463

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07 Sep 2008, 20:36
ttwang56 wrote:
IMO C?

I don't think I did it the right way but i just ended up trying some numbers out

1+2+3+4 = 10
2+4+6+8 = 20

2+3+4+5+6 =20
2+4+6+8+10 = 30

whats the OA and what is another way to solve? thanks

Agree on C. Solved by picking numbers as well.
SVP
Joined: 17 Jun 2008
Posts: 1529

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07 Sep 2008, 21:01
Sum of first n positive integers = 1 + 2 + 3 +.... + n = S.

Sum of first n positive even integers = 2 + 4 + 6 + ...... + 2n
= 2(1+2+3+....+n) = 2S.
Intern
Joined: 26 Jan 2008
Posts: 26

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08 Sep 2008, 10:15
scthakur wrote:
Sum of first n positive integers = 1 + 2 + 3 +.... + n = S.

Sum of first n positive even integers = 2 + 4 + 6 + ...... + 2n
= 2(1+2+3+....+n) = 2S.

ah i was adding 1 and not 2. thanks.
Re: Tricky one   [#permalink] 08 Sep 2008, 10:15
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If the sum of the first n positive integers is S, what is

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