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3^(-n)*3^(-n) = 1/81, what is the value of n?

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Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42571

Kudos [?]: 135380 [0], given: 12691

3^(-n)*3^(-n) = 1/81, what is the value of n? [#permalink]

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New post 12 Nov 2017, 00:03
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

90% (00:24) correct 10% (00:02) wrong based on 49 sessions

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Kudos [?]: 135380 [0], given: 12691

Expert Post
Math Expert
User avatar
D
Joined: 02 Aug 2009
Posts: 5341

Kudos [?]: 6107 [0], given: 121

Re: 3^(-n)*3^(-n) = 1/81, what is the value of n? [#permalink]

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New post 12 Nov 2017, 04:19
Bunuel wrote:
\(3^{-n}*3^{-n} = \frac{1}{81}\), what is the value of n?

(A) -2

(B) 0

(C) 1

(D) 2

(E) 4



\(x^{-y}=\frac{1}{x^y}\)...
\(3^{-n}*3^{-n}=3^{-n-n}=3^{-2n}=\frac{1}{3^{2n}}=\frac{1}{81}=\frac{1}{3^4}\)

So 2n=4.....n=2
D
_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

Kudos [?]: 6107 [0], given: 121

VP
VP
avatar
P
Joined: 22 May 2016
Posts: 1113

Kudos [?]: 397 [0], given: 640

3^(-n)*3^(-n) = 1/81, what is the value of n? [#permalink]

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New post 12 Nov 2017, 08:57
Bunuel wrote:
\(3^{-n}*3^{-n} = \frac{1}{81}\), what is the value of n?

(A) -2

(B) 0

(C) 1

(D) 2

(E) 4

\(3^{-n}*3^{-n} = \frac{1}{81}\)

\(3^{-n}*3^{-n} = \frac{1}{3^4}\)

\(3^{-n}*3^{-n} = 3^{-4}\)

\(-n + (-n) = -4\)
\(-2n = -4\)
\(n = 2\)

Answer D

Kudos [?]: 397 [0], given: 640

3^(-n)*3^(-n) = 1/81, what is the value of n?   [#permalink] 12 Nov 2017, 08:57
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