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The sequence a1,a2,a3....an of n integers is such that ak =

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GMAT Club Legend
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The sequence a1,a2,a3....an of n integers is such that ak = [#permalink] New post 29 Aug 2007, 19:56
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

The sequence a1,a2,a3....an of n integers is such that ak = k if k is odd, and ak = -a(k-1) if k is even. Is the sum of the terms in teh sequence positive?

1) n is odd
2) an is positive

Note: -a(k-1) (the (k-1) is a subscript)
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 [#permalink] New post 29 Aug 2007, 23:35
sequence : 1, -1 , 3 , -3 , 5 , -5 .....

if n is odd the sum will always be pisitive as last term would be positive..and all previous terms would cancel out

an is positive means that sum is positive as all the previous terms cancel out.

ans : D
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 [#permalink] New post 30 Aug 2007, 15:00
I get D too..

here is my rational

0 is even..

a0=-(0-1)=+1

now if N is even..the sum will of integers cancel out except for leaving 1 behind (accounting for 0)

if N is odd the sum is still positive

if N is even, sum is still positive..it will be 1
  [#permalink] 30 Aug 2007, 15:00
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The sequence a1,a2,a3....an of n integers is such that ak =

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