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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]

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New post 07 Sep 2008, 20:38
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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Intern
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Re: Tricky one [#permalink]

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New post 07 Sep 2008, 20:44
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

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Senior Manager
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Re: Tricky one [#permalink]

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New post 07 Sep 2008, 21:36
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.

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SVP
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Re: Tricky one [#permalink]

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New post 07 Sep 2008, 22:01
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.

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Intern
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Re: Tricky one [#permalink]

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New post 08 Sep 2008, 11:15
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.

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Re: Tricky one   [#permalink] 08 Sep 2008, 11:15
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If the sum of the first n positive integers is S, what is

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