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a1 = 7 a2 = 8 a3 = 10

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Manager
Joined: 04 Jun 2011
Posts: 193
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Kudos [?]: 32 [0], given: 21

a1 = 7 a2 = 8 a3 = 10 [#permalink]  11 Sep 2011, 03:57
00:00

Difficulty:

(N/A)

Question Stats:

75% (00:00) correct 25% (03:46) wrong based on 4 sessions

I have a curious question... quite honesly i did not understand what an= a_(n-3) +7 meant... i assumed something got cut off maybe it was a1*(n-3) + 7

i am used to seeing a(n) = a(n-3) +7
or watching the "n-3" similar to the "n" (as a footer) in the question in my quant thus far

so my questions are...

1. so do we get to see such a thing on the real test? i mean should i get used to this convention? and most importantly are there others?

2. if not, i would appreciate if the Veritas instructors have a look at this and help make the question more clearer

Thanks!
[Reveal] Spoiler: OA

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Joined: 01 Feb 2011
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Kudos [?]: 82 [1] , given: 42

Re: a1 = 7 a2 = 8 a3 = 10 [#permalink]  11 Sep 2011, 07:50
1
KUDOS
I am sure that's just a typo. it means a(n) = a(n-3)+7.

Given a1 = 7 , a2 =8, a3 =10

1. Sufficient

n is multiple of 3.

a3 = 10
a6 = a3+7
a9 = a6+7 = a3+2*7
a12 = a3+3*7

so basically remainder of a(n) when n is divided by 7 and when n is multiple of 3 = remainder of a3 when its
divided by 7
= remainder of (10/7) = 3

2. Not sufficient

a2 = 8, remainder of a2/7 = 1
a4 =a1+7 = 14;=>remainder of 14/7= 0

Senior Manager
Joined: 03 Mar 2010
Posts: 446
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Kudos [?]: 109 [0], given: 22

Re: a1 = 7 a2 = 8 a3 = 10 [#permalink]  12 Sep 2011, 02:47
Write few elements of series
a1=7
a2=8
a3=10
a4=a1+7=14
a5=a2+7=15
a6=a3+7=17
a7=a4+7=21
a8=a5+7=22
a9=a6+7=24

Stmt1: n is a multiple of 3.
a3,a6,a9 all leaving remainder of 3.
Sufficient.

Stmt2: n is an even number
a2=8 leaves remainder 1
a4=14 leaves remainder 0.
Not sufficient.

OA A.
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Re: a1 = 7 a2 = 8 a3 = 10 [#permalink]  12 Sep 2011, 03:15
Yes.. I was dumbstruck for a moment when I saw this question in the test. But it can only be a(n-3).. So I went ahead and solved it that way..
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Kudos [?]: 4868 [0], given: 163

Re: a1 = 7 a2 = 8 a3 = 10 [#permalink]  13 Sep 2011, 21:16
Expert's post
viks4gmat wrote:

I have a curious question... quite honesly i did not understand what an= a_(n-3) +7 meant... i assumed something got cut off maybe it was a1*(n-3) + 7

i am used to seeing a(n) = a(n-3) +7
or watching the "n-3" similar to the "n" (as a footer) in the question in my quant thus far

so my questions are...

1. so do we get to see such a thing on the real test? i mean should i get used to this convention? and most importantly are there others?

2. if not, i would appreciate if the Veritas instructors have a look at this and help make the question more clearer

Thanks!

Yes, it is a typo. Subscripts and superscripts behave differently in different software and hence such errors creep up sometimes. You should not see such a thing in actual GMAT but if you do, think what it should be.
Since you have subscripts on A everywhere, this logically seems like a subscript. Anyway, we know that '_' is not a mathematical symbol and in series questions, more often than not, subsequent terms are related to previous terms through some relation.
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Manager
Joined: 04 Jun 2011
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Kudos [?]: 32 [0], given: 21

Re: a1 = 7 a2 = 8 a3 = 10 [#permalink]  17 Sep 2011, 02:29
Thanks Karishma.. yup.. i agree that some errors can creep in no matter what.... Murphy's law!!

was just curious if this denotes something i dont know...
on recognizing this as a subscript.... well i went a step ahead to assume its a1 whose head was cut off from the base so i think too much thinking cost me this question
Re: a1 = 7 a2 = 8 a3 = 10   [#permalink] 17 Sep 2011, 02:29
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