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# If 8x=2^y, what is the value of x, in terms of y?

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Math Revolution GMAT Instructor
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If 8x=2^y, what is the value of x, in terms of y?  [#permalink]

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06 Oct 2017, 02:44
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92% (00:47) correct 8% (00:59) wrong based on 65 sessions

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[GMAT math practice question]

If $$8x=2^y$$, what is the value of x, in terms of y?

A. $$x=2^{3y-2}$$
B. $$x=4y$$
C. $$x=4^{y-2}$$
D. $$x=2^{y-3}$$
E. $$x=2y$$

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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Senior Manager Joined: 06 Jan 2015 Posts: 441 Location: India Concentration: Operations, Finance GPA: 3.35 WE: Information Technology (Computer Software) Re: If 8x=2^y, what is the value of x, in terms of y? [#permalink] ### Show Tags 06 Oct 2017, 04:26 MathRevolution wrote: [GMAT math practice question] If $$8x=2^y$$, what is the value of x, in terms of y? A. $$x=2^{3y-2}$$ B. $$x=4y$$ C. $$x=4^{y-2}$$ D. $$x=2^{y-3}$$ E. $$x=2y$$ $$8x=2^y$$ ==> $$2^3x=2^y$$ ==> $$x=2^y/(2^3)$$ ==>$$x=2^{y-3}$$ Ans - D _________________ आत्मनॊ मोक्षार्थम् जगद्धिताय च Resource: GMATPrep RCs With Solution Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6027 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: If 8x=2^y, what is the value of x, in terms of y? [#permalink] ### Show Tags 08 Oct 2017, 18:05 => $$8x = 2^y ⬄ 2^3x = 2^y ⬄ x = 2^{y-3}$$ Answer : D _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
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Re: If 8x=2^y, what is the value of x, in terms of y?  [#permalink]

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17 Jul 2018, 08:36
Top Contributor
MathRevolution wrote:
[GMAT math practice question]

If $$8x=2^y$$, what is the value of x, in terms of y?

A. $$x=2^{3y-2}$$
B. $$x=4y$$
C. $$x=4^{y-2}$$
D. $$x=2^{y-3}$$
E. $$x=2y$$

Another approach is to find some values of x and y that satisfy the given equation 8x = 2^y
One solution that works is x = 1 and y = 3, since 8(1) = 2^3
Now take each answer choice and replace x and y with 1 and 3 respectively and see which one yields a true equation:

A. 1 = 2^[3(3) - 2] Not true. ELIMINATE
B. 1 = 4(3) Not true. ELIMINATE
C. 1 = 4^(3 - 2) Not true. ELIMINATE
D. 1 = 2^(3 - 3) True. KEEP!
E. 1 = 2(3) Not true. ELIMINATE

Cheers,
Brent
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Re: If 8x=2^y, what is the value of x, in terms of y?  [#permalink]

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19 Jul 2018, 16:57
MathRevolution wrote:
[GMAT math practice question]

If $$8x=2^y$$, what is the value of x, in terms of y?

A. $$x=2^{3y-2}$$
B. $$x=4y$$
C. $$x=4^{y-2}$$
D. $$x=2^{y-3}$$
E. $$x=2y$$

Simplifying, we have:

2^3 * x = 2^y

x = 2^y / 2^3

x = 2^(y - 3)

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Re: If 8x=2^y, what is the value of x, in terms of y? &nbs [#permalink] 19 Jul 2018, 16:57
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