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# M15 #3

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Math Expert
Joined: 02 Sep 2009
Posts: 41886

Kudos [?]: 128753 [0], given: 12182

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05 Feb 2012, 07:29
akhilright wrote:
Thanks Bunuel,
I understood that particular reply, but fundamentaly i did not get how has the reply reworded A (n+1)=An/n+1, from the real equation given in the question

First of all, if you look at the formula given in the initial post and the one given in mine, you'll notice that they're basically the same: just replaced n with n+1. Next, I didn't reworded the question, I changed it so that it would be more GMAT type.
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Kudos [?]: 128753 [0], given: 12182

VP
Status: Been a long time guys...
Joined: 03 Feb 2011
Posts: 1377

Kudos [?]: 1675 [0], given: 62

Location: United States (NY)
Concentration: Finance, Marketing
GPA: 3.75

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07 Jan 2013, 06:13
Bunuel.
Since its given that n>1, then how can we even deal with A1.
This is why I got this one wrong.
Chose A, which is wrong.
_________________

Kudos [?]: 1675 [0], given: 62

VP
Status: Been a long time guys...
Joined: 03 Feb 2011
Posts: 1377

Kudos [?]: 1675 [0], given: 62

Location: United States (NY)
Concentration: Finance, Marketing
GPA: 3.75

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07 Jan 2013, 06:27
Sorry for being dumb.
But then why we deal with even $$A$$1. For all n>1, the series must start with $$A$$2?
Regards.
_________________

Kudos [?]: 1675 [0], given: 62

Math Expert
Joined: 02 Sep 2009
Posts: 41886

Kudos [?]: 128753 [0], given: 12182

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07 Jan 2013, 06:52
Marcab wrote:
Sorry for being dumb.
But then why we deal with even $$A$$1. For all n>1, the series must start with $$A$$2?
Regards.

The sequence starts with A1, naturally. But we have formula that gives the terms starting from A2. It's a common way of defining sequences, for example check these questions from MGMAT:
sequence-s-is-defined-as-sn-sn-1-1-1-sn-1-1-for-all-n-144382.html
sn-2sn-1-4-and-qn-4qn-1-8-for-all-n-1-if-s5-q4-125965.html

More questions on sequences to practice:
search.php?search_id=tag&tag_id=112 (PS)
search.php?search_id=tag&tag_id=111(DS)
_________________

Kudos [?]: 128753 [0], given: 12182

VP
Status: Been a long time guys...
Joined: 03 Feb 2011
Posts: 1377

Kudos [?]: 1675 [0], given: 62

Location: United States (NY)
Concentration: Finance, Marketing
GPA: 3.75

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07 Jan 2013, 07:13
In fact I did such questions but it was not mentioned that n>1. Thats why there was no problem in doing questions where even finding other values was not at all confusing.
But I am unable to recover from the shock that this question gave.
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Intern
Joined: 30 May 2011
Posts: 18

Kudos [?]: 7 [0], given: 4

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04 Feb 2013, 17:39
I was a bit confused on what the question is asking. I thought it was asking n could be a lot of number, and how many of those n could equal to 1/2...

Kudos [?]: 7 [0], given: 4

Manager
Joined: 20 Oct 2013
Posts: 75

Kudos [?]: 12 [0], given: 15

Location: United States
Concentration: General Management, Real Estate

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20 Apr 2014, 08:21
Elements of this series gradually get smaller when n increases. Knowing 1 element would let us calculate the others, so definitely we will know how many is smaller than 1/2
1) is sufficient. 2) lets us to know the value of A2, so also sufficient.

Choose d

Kudos [?]: 12 [0], given: 15

Re: M15 #3   [#permalink] 20 Apr 2014, 08:21

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# M15 #3

Moderator: Bunuel

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