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To find the edge of the cube

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by gmattesttaker2 » Sat Feb 15, 2014 11:05 pm
Hello,

Can you please tell me if my answer for the following is correct:


What is the edge of a cube whose surface area is 21?


Let e be the edge of the cube. Total surface area = 6e^2

6e^2 = 21 => e^2 = 21/6

=> e = [spoiler]sq.root ( 21/6 )[/spoiler]

Thanks,
Sri
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by Patrick_GMATFix » Sat Feb 15, 2014 11:34 pm
Correct.
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by [email protected] » Sun Feb 16, 2014 1:10 am
Hi Sri,

Yes, your logic and math are correct. Most geometry questions are based on a handful of standard formulas. While some geometry questions can be complicated (multi-shape geometry, certain graphing questions), for the most part if you know the formulas then you can answer the questions with "math." In certain situations, you can TEST Values or TEST THE ANSWERS, but geometry is primarily formulaic work. Make sure that you have your formulas memorized and you should be able to pick up most (if not all) of the Geometry points on Test Day.

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by Abhishek009 » Sun Feb 16, 2014 8:10 am
gmattesttaker2 wrote:Hello,

Can you please tell me if my answer for the following is correct:


What is the edge of a cube whose surface area is 21?


Let e be the edge of the cube. Total surface area = 6e^2

6e^2 = 21 => e^2 = 21/6

=> e = [spoiler]sq.root ( 21/6 )[/spoiler]

Thanks,
Sri
Correct , I would go on further -

e^2 = 21/6

Or, e^2 = 7/3

or, e = √ 7/3 => √ 2.33
Abhishek
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