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Geometry

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Intern
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Joined: 02 Jan 2015
Posts: 8
Geometry  [#permalink]

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New post 17 Jan 2015, 13:57
00:00
A
B
C
D
E

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A cube has length x, a surface area y, and a volume z. Which of the following must be true?

A. xy/z - y/x = 0
B. x^2y/z - y/x = 0
C. xz/x^2y - x^2/xy = 0
D. x(√y)/√z - x^2/y = 0
E. (√z)/xy - (√y)/x^2 = 0

Is there a simpler way to solve this rather than taking individual value combinations and checking each option.

Regards,

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Director
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Status: Tutor - BrushMyQuant
Joined: 05 Apr 2011
Posts: 612
Location: India
Concentration: Finance, Marketing
Schools: XLRI (A)
GMAT 1: 700 Q51 V31
GPA: 3
WE: Information Technology (Computer Software)
Re: Geometry  [#permalink]

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New post 17 Jan 2015, 21:57
1
We can solve it using units
If x is in m(meters) then y will be m^2 then z will be m^3

A cannot be true as m*m^2/m^3 - m^2/m.. first entity does not have a unit so you cannot subtract it from the second unit which has meter unit
B Can be true as it is meter - meter
C cannot be true : No unit - Meter unit
D cannot be true: √meter unit - no unit
E cannot be true: 1/meter*√meter unit - 1/meter unit

So, answer will be B

Hope it helps!
amidamani13 wrote:
A cube has length x, a surface area y, and a volume z. Which of the following must be true?

A. xy/z - y/x = 0
B. x^2y/z - y/x = 0
C. xz/x^2y - x^2/xy = 0
D. x(√y)/√z - x^2/y = 0
E. (√z)/xy - (√y)/x^2 = 0

Is there a simpler way to solve this rather than taking individual value combinations and checking each option.

Regards,

_________________

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How to Solve :
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Intern
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Joined: 02 Jan 2015
Posts: 8
Re: Geometry  [#permalink]

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New post 19 Jan 2015, 01:10
Thanks a ton...really helpful....:) :)

Regards,
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Joined: 12 Jun 2016
Posts: 219
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Geometry  [#permalink]

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New post 06 May 2017, 22:25
Hello BrushMyQuant,

A very innovative way for solving indeed! Thanks for sharing. Hope solutions like this "Come" to me when I sit to solve. :-D

Specially, even if I plugged in numbers (X=1, Y=6 and Z=1) Both B & C very true. Again I had to Pick (X=2, Y=24 and Z=8) to see that B is the only answer. It took me approximate 3 Mins to do this :x

Thanks again for this approach!

BrushMyQuant wrote:
We can solve it using units
If x is in m(meters) then y will be m^2 then z will be m^3

A cannot be true as m*m^2/m^3 - m^2/m.. first entity does not have a unit so you cannot subtract it from the second unit which has meter unit
B Can be true as it is meter - meter
C cannot be true : No unit - Meter unit
D cannot be true: √meter unit - no unit
E cannot be true: 1/meter*√meter unit - 1/meter unit

So, answer will be B

Hope it helps!
amidamani13 wrote:
A cube has length x, a surface area y, and a volume z. Which of the following must be true?

A. xy/z - y/x = 0
B. x^2y/z - y/x = 0
C. xz/x^2y - x^2/xy = 0
D. x(√y)/√z - x^2/y = 0
E. (√z)/xy - (√y)/x^2 = 0

Is there a simpler way to solve this rather than taking individual value combinations and checking each option.

Regards,

_________________

My Best is yet to come!

Director
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Affiliations: GMATQuantum
Joined: 19 Apr 2009
Posts: 605
Re: Geometry  [#permalink]

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New post 07 May 2017, 07:24
1
Top Contributor

Hi amidamani13,

This is a poorly written GMAT question, and I am pretty certain that this is not an official GMAT question. If the GMAT writers created such a question they will make sure that the units are consistent so one could not just look at the dimensions of the answer choices and eliminate answers.

The image I have attached is a one of the official GMAT questions that came to my mind when I saw this question. It is a bit different and not terribly difficult but you will see that it is well written.

Cheers,
Dabral


--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

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Re: Geometry &nbs [#permalink] 07 May 2017, 07:24
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