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The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for
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30 Jan 2014, 00:50
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89% (00:57) correct 11% (01:02) wrong based on 1053 sessions
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The Official Guide For GMAT® Quantitative Review, 2ND EditionThe sequence \(a_1\), \(a_2\), \(a_3\), \(a_4\), \(a_5\) is such that \(a_n= a_{n1} + 5\) for \(2\leq n \leq 5\). If \(a_5 = 31\), what is the value of \(a_1\) ? (A) 1 (B) 6 (C) 11 (D) 16 (E) 21 Problem Solving Question: 67 Category: Algebra Sequences Page: 70 Difficulty: 600 GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition  Quantitative Questions ProjectEach week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution. We'll be glad if you participate in development of this project: 1. Please provide your solutions to the questions; 2. Please vote for the best solutions by pressing Kudos button; 3. Please vote for the questions themselves by pressing Kudos button; 4. Please share your views on difficulty level of the questions, so that we have most precise evaluation. Thank you!
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Math Expert
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The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for
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30 Jan 2014, 00:50



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Re: The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for
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30 Jan 2014, 02:10
The sequence \(a_1\), \(a_2\), \(a_3\), \(a_4\), \(a_5\) is such that \(a_n= a_{n1} + 5\) for \(2\leq n \leq 5\). If \(a_5 = 31\), what is the value of \(a_1\) ? (A) 1 (B) 6 (C) 11 (D) 16 (E) 21 Sol: Given a5=31....and also a5=a4+5 > a4=26> a3=21>a2=16 >a1=11. Ans C 600 level is okay
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Re: The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for
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30 Jan 2014, 02:31
Ans.C This is nothing but an AP with common diff=5 a5=31, a4=26 a3=21, a2=16, a1=11
a5=a1+4d 31=a1+4*5 3120=a1=11



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Re: The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for
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30 Jan 2014, 09:42
This answer can be easily be solve by A.P. The sequence is an A.P. with each term at an increment of 5 from the previous term. So a5 is nothing but a1+20.
a5=a1+20=31 => a1=11.
Answer is C



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Re: The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for
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31 Jan 2014, 05:13
The sequence \(a_1, a_2, a_3, a_4, a_5\) is such that \(a_n= a_{n1} + 5\) for \(2\leq n \leq 5\). If \(a_5 = 31\), what is the value of \(a_1\) ?
(A) 1 (B) 6 (C) 11 (D) 16 (E) 21
Given sequence is A.P. with common difference of 5. Last Term  First Term = (Number of terms 1)* common difference
\(a_5a_1 = (51)*\) \(common\) \(difference\)
Or, \(31a_1=(51)*5\)
Or, \(a_1=3120=11\)
Answer: (C)



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Re: The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for
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18 Mar 2014, 22:12
Bunuel wrote: SOLUTION
The sequence \(a_1\), \(a_2\), \(a_3\), \(a_4\), \(a_5\) is such that \(a_n= a_{n1} + 5\) for \(2\leq n \leq 5\). If \(a_5 = 31\), what is the value of \(a_1\) ?
(A) 1 (B) 6 (C) 11 (D) 16 (E) 21
\(a_5 = 31\); \(a_4 =315=26\); \(a_3 =265=21\); \(a_2 =215=16\); \(a_1 =165=1\).
Answer: C. But 2<= n <= 5 so how is this applicable to a1 i.e. n=1?



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Re: The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for
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19 Mar 2014, 00:59



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Re: The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for
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14 May 2015, 14:25
5 is constant here so > a5  4*5 = 11 (4*5 because we have 4 numbers between a5 and a1 ... a4,3,2,1 )
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Re: The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for
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04 May 2016, 02:40
a5 = 31 a4 = 315 = 26 a3 = 26  5 = 21 a2 = 21  5 = 16 a1 = 16  5 = 11 correct answer  C



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Re: The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for
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26 Mar 2018, 16:34
Quote: The sequence \(a_1\), \(a_2\), \(a_3\), \(a_4\), \(a_5\) is such that \(a_n= a_{n1} + 5\) for \(2\leq n \leq 5\). If \(a_5 = 31\), what is the value of \(a_1\) ?
(A) 1 (B) 6 (C) 11 (D) 16 (E) 21
a(5) = 31, so: a(5) = a(4) + 5 31 = a(4) + 5 26 = a(4) The pattern is to subtract 5 to obtain the value of the previous term in this recursivelydefined sequence. Thus, a(3) = 21, a(2) =16, and a(1) = 11. Answer: C
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Re: The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for
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20 Oct 2018, 03:11
a5 = a4 + 5 a4 = a3 + 5 a3 = a2 + 5 a2 = a1 + 5
so a1 = a5  4*5 = 31  20 = 11
Answer choice C




Re: The sequence a1, a2, a3, a4, a5 is such that an=a(n1)+5 for &nbs
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20 Oct 2018, 03:11






