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The sequence s1, s2, s3, ..., sn, ... is such that Sn= 1/n - 1/(n + 1)

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Re: The sequence s1, s2, s3, ..., sn, ... is such that Sn= 1/n - 1/(n + 1)  [#permalink]

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New post 16 Jul 2017, 09:39
Solve it by identifying the Pattern
S1 = 1/2
S2 = 1/6 => S1 +S2 = (1/2 + 1/6) = 2/3
S3 = 1/12 => ((S1+S2) + S3) = (2/3 + 1/12) = 3/4
S4 = 1/20 => ((S1+S2+S3) + S4) = (3/4 + 1/20) = 4/5
.
.
and so on

Option (a) => k>10
As per the pattern above sum until S9 = 9/10 and S10 = 10/11 , so k>10 will always be greater than 9/10
Sufficient

Option (b) => K<19
As per pattern above, clearly sum of k terms will be greater than 9/10 for 9<K<19 and lesser than or equal to 9/10 for 1=<K <=9 .
InSufficient
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Re: The sequence s1, s2, s3, ..., sn, ... is such that Sn= 1/n - 1/(n + 1)  [#permalink]

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New post 21 Jul 2018, 08:25
Bunuel gmatbusters

This question is a duplicate of this Q (https://gmatclub.com/forum/the-sequence ... ml?kudos=1) and hence, it should be moved to the archive forum. Otherwise, having both same questions in this forum would beat the purpose of the timer icon (green or red) that shows whether one's attempted a question before.
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Everything You Need To Know About Verb Tenses

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Re: The sequence s1, s2, s3, ..., sn, ... is such that Sn= 1/n - 1/(n + 1)  [#permalink]

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New post 21 Jul 2018, 08:27
Bunuel gmatbusters

This question is a duplicate of this Q (https://gmatclub.com/forum/the-sequence ... ml?kudos=1) and hence, it should be moved to the archive forum. Otherwise, having both same questions in this forum would beat the purpose of the timer icon (green or red) that shows whether one's attempted a question before.
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Everything You Need To Know About Verb Tenses

Re: The sequence s1, s2, s3, ..., sn, ... is such that Sn= 1/n - 1/(n + 1) &nbs [#permalink] 21 Jul 2018, 08:27

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