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If x^2 = 2y^3 and 2y = 4, what is the value of x^2 + y?

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Manager
Joined: 22 Mar 2012
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Location: United States (NY)
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If x^2 = 2y^3 and 2y = 4, what is the value of x^2 + y?  [#permalink]

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Updated on: 24 Aug 2012, 21:39
2
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5% (low)

Question Stats:

93% (00:31) correct 7% (00:56) wrong based on 113 sessions

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If x^2 = 2y^3 and 2y = 4, what is the value of x^2 + y?

A. -14
B. -2
C. 3
D. 6
E. 18

I understand how they came to the answer. But I'm confused as to why I can't replace 2y in the first equation with 4 to get x^2 = 64. That would give the equation x^2 + y, value of 66. Please tell me what am I missing? Attaching the screenshot of the question and answer. This is from the GMAC software.

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Originally posted by KAS1 on 24 Aug 2012, 13:36.
Last edited by Bunuel on 24 Aug 2012, 21:39, edited 1 time in total.
Edited the question.
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Joined: 22 Mar 2011
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24 Aug 2012, 13:49
KAS1 wrote:
If x^2 = 2y^3 and 2y = 4, what is the value of x^2 + y?

A. -14
B. -2
C. 3
D. 6
E. 18

I understand how they came to the answer. But I'm confused as to why I can't replace 2y in the first equation with 4 to get x^2 = 64. That would give the equation x^2 + y, value of 66. Please tell me what am I missing? Attaching the screenshot of the question and answer. This is from the GMAC software.

In the equation it is $$2y^3$$ and not $$(2y)^3.$$ Therefore $$2y^3=2*2^3=16,$$ because from $$2y=4,$$we obtain $$y=2.$$
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Manager
Joined: 22 Mar 2012
Posts: 85
Location: United States (NY)
Concentration: General Management, Marketing
GPA: 3.1
WE: Accounting (Other)

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24 Aug 2012, 19:04
Wow!
Thanks so much. I have to pay attention to these little things on the exam.
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Re: If x^2 = 2y^3 and 2y = 4, what is the value of x^2 + y?  [#permalink]

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05 Sep 2018, 11:11
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Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: If x^2 = 2y^3 and 2y = 4, what is the value of x^2 + y? &nbs [#permalink] 05 Sep 2018, 11:11
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