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2^x = 7, then 2^2x =? a)49 b)7 c)128 d)64 e)32 Please assist with a

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2^x = 7, then 2^2x =? a)49 b)7 c)128 d)64 e)32 Please assist with a  [#permalink]

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New post 29 Sep 2016, 09:40
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2^x = 7, then 2^2x =?

A) 49
B) 7
C) 128
D) 64
E) 32

Please assist with above problem.
Magoosh GMAT Instructor
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Posts: 4493
2^x = 7, then 2^2x =? a)49 b)7 c)128 d)64 e)32 Please assist with a  [#permalink]

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New post 29 Sep 2016, 10:23
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1
alanforde800Maximus wrote:
2^x = 7, then 2^2x =?

A) 49
B) 7
C) 128
D) 64
E) 32

Please assist with above problem.

Dear alanforde800Maximus,

I'm happy to respond. :-)

Here, we have to be comfortable with the laws of exponents. For example, A^(pq) = (A^p)^q. That's a very important patterns to know.

Here, 2^(2x) can be rewritten as (2^x)^2. Since, we know that 2^x = 7, we know that (2^x)^2 = 49. Answer = (A).

Here are some GMAT Math Flashcards you might find helpful.

Does this make sense?
Mike :-)
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Mike McGarry
Magoosh Test Prep


Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)

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Re: 2^x = 7, then 2^2x =? a)49 b)7 c)128 d)64 e)32 Please assist with a  [#permalink]

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New post 27 Feb 2017, 04:42
2^2x = 2^x * 2^x = 7*7 = 49
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Re: 2^x = 7, then 2^2x =? a)49 b)7 c)128 d)64 e)32 Please assist with a  [#permalink]

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New post 18 Oct 2018, 21:20
For this question

\(2^x = 7\)

We have to find (2)^2x

Now we can write 2^2x as \((2^x)^2\)

Which will imply \(7^2\)

Giving answer as A
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Re: 2^x = 7, then 2^2x =? a)49 b)7 c)128 d)64 e)32 Please assist with a &nbs [#permalink] 18 Oct 2018, 21:20
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