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Director  Joined: 16 May 2014
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GRE Math Challenge #10- The nth term of the sequence a 1 , a [#permalink]
Expert's post 00:00

Question Stats: 92% (00:30) correct 7% (00:53) wrong based on 77 sessions

The nth term of the sequence $$a_{1}$$ , $$a_{2}$$ , $$a_{3}$$ , …, an is defined as $$a_{n} = - (a_{n - 1} )$$. The first term $$a_{1} = – 1$$.

 Quantity A Quantity B $$a_{5}$$ $$1$$

A. The quantity in Column A is greater
B. The quantity in Column B is greater
C. The two quantities are equal
D. The relationship cannot be determined from the information given

Kudos for the right answer and solution.
[Reveal] Spoiler: OA

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If you find this post helpful, please press the kudos button to let me know !  Intern Joined: 18 Jun 2014
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Re: GRE Math Challenge #10 [#permalink]
1
KUDOS
Using a1 = -1, we get a2 = (-)a1 = 1
similarly a3 would be -1. Therefore, the odd nos. in the series will be (-)1 and even nos. will be 1.
Hence, a5 = (-)1. Column (B) is greater than Column (A).

The correct answer would be (B)
Manager Joined: 03 Dec 2017
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Re: GRE Math Challenge #10- The nth term of sequence [#permalink]
a odd are -1
a even are 1
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The nth term of the sequence a 1 , a 2 , a 3 , …, a n is def [#permalink]
Expert's post

The nth term of the sequence $$a_{1}$$ , $$a_{2}$$ , $$a_{3}$$ , …, an is defined as $$a_{n} = - (a_{n - 1} )$$. The first term $$a_{1} = – 1$$.

 Quantity A Quantity B $$a_{5}$$ $$1$$

A. The quantity in Column A is greater
B. The quantity in Column B is greater
C. The two quantities are equal
D. The relationship cannot be determined from the information given

Kudos for the right answer and solution.
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Re: The nth term of the sequence a 1 , a 2 , a 3 , …, a n is def [#permalink]
1
KUDOS
On resolving we would get a sequence where all odd numbers in the series would be -1 and all even numbers would be +1. So a1, a3, a5, ..so on have values -1. a2, a4, a6, ... so on have +1.

Hence B is greater as a5 would have value of -1
Manager Joined: 27 Feb 2017
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Re: The nth term of the sequence a 1 , a 2 , a 3 , …, a n is def [#permalink]
can someone please explain this. I do not understand how we solve the terms Retired Moderator Joined: 07 Jun 2014
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Re: The nth term of the sequence a 1 , a 2 , a 3 , …, a n is def [#permalink]
2
KUDOS
Expert's post
It is given that $$a_{1}=-1$$ and $$a_{n}=-a_{n-1}$$.

So $$a_{2}=-a_{1}=1$$.

And $$a_{3}=-a_{2}=-1$$.

So we can see every odd term is -1 and every even term is +1. So $$a_{5]$$ must be -1.

Hence option B is correct!
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Re: The nth term of the sequence a 1 , a 2 , a 3 , …, a n is def [#permalink]
Carcass wrote:
The nth term of the sequence a 1 , a 2 , a 3 , …, an is defined as $$a_{n} = -(a_{n - 1} )$$. The first term a1 equals –1.

 Quantity A Quantity B a5 1

A. The quantity in Column A is greater
B. The quantity in Column B is greater
C. The two quantities are equal
D. The relationship cannot be determined from the information given

Kudos for the right answer and solution.

Intern  Joined: 04 May 2017
Posts: 36
Followers: 0

Kudos [?]: 30 , given: 6

Re: The nth term of the sequence a 1 , a 2 , a 3 , …, a n is def [#permalink]
The sequence: -1 1 -1 1 -1 -> a5 = -1 -> B.
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Manager Joined: 23 Oct 2018
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Re: The nth term of the sequence a 1 , a 2 , a 3 , …, a n is def [#permalink]
thanks for the explanation Re: The nth term of the sequence a 1 , a 2 , a 3 , …, a n is def   [#permalink] 25 Oct 2018, 01:37
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