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Is 81^a=3^9(b-1)?

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Joined: 06 Jul 2014
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Concentration: Finance, Entrepreneurship
GMAT 1: 640 Q48 V30
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Is 81^a=3^9(b-1)? [#permalink]

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New post 17 Aug 2017, 10:22
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Question Stats:

78% (00:45) correct 22% (00:32) wrong based on 45 sessions

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Is 81^a=3^(b-1)?

1) 3a+1=b-a
2) a=3
[Reveal] Spoiler: OA

Kudos [?]: 40 [1], given: 179

Director
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P
Joined: 25 Feb 2013
Posts: 619

Kudos [?]: 305 [0], given: 39

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Re: Is 81^a=3^9(b-1)? [#permalink]

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New post 17 Aug 2017, 10:40
Bounce1987 wrote:
Is 81^a=3^(b-1)?

1) 3a+1=b-a
2) a=3


\(81^a\) \(=3^{(b-1)}\)
\(3^{4a} = 3^{(b-1)}\) or \(4a = b-1\)

Statement 1: \(3a+1=b-a\), this implies \(4a = b-1\). Sufficient

Statement 2: does not provide any value of \(b\). Hence Not Sufficient

Option \(A\)

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Joined: 06 Jul 2016
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Kudos [?]: 127 [0], given: 98

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Concentration: Strategy, Finance
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Re: Is 81^a=3^9(b-1)? [#permalink]

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New post 17 Aug 2017, 10:59
Bounce1987 wrote:
Is 81^a=3^(b-1)?


\(81^a\) = 3^(b-1)
=> 3^(4a) = 3^(b-1)
=> 4a = b-1 ?

Quote:
1) 3a+1=b-a
2) a=3


1) 3a + a = b-1
=> 4a = b - 1
Sufficient.

2) a = 3
we know nothing about B.
Insufficient.

A is the answer.
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Kudos [?]: 127 [0], given: 98

Re: Is 81^a=3^9(b-1)?   [#permalink] 17 Aug 2017, 10:59
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