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# What is the length of the sides of a given cube?

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
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GMAT 1: 760 Q51 V42
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What is the length of the sides of a given cube?  [#permalink]

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23 Aug 2018, 01:11
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Difficulty:

15% (low)

Question Stats:

85% (00:30) correct 15% (00:50) wrong based on 46 sessions

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[Math Revolution GMAT math practice question]

What is the length of the sides of a given cube?

1) The surface area of the cube is $$150$$
2) The volume of the cube is $$125$$

_________________

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 $149 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Director Status: Learning stage Joined: 01 Oct 2017 Posts: 950 WE: Supply Chain Management (Energy and Utilities) Re: What is the length of the sides of a given cube? [#permalink] ### Show Tags 23 Aug 2018, 01:17 MathRevolution wrote: [Math Revolution GMAT math practice question] What is the length of the sides of a given cube? 1) The surface area of the cube is $$150$$ 2) The volume of the cube is $$125$$ St1:- Surface area of cube =150 Or, $$6a^2=150$$ 'a' can be determined. Sufficient St2:- Volume of the cube=125 Or, $$a^3$$=125 'a' can be determined. Sufficient. Ans. (D) _________________ Regards, PKN Rise above the storm, you will find the sunshine CEO Joined: 11 Sep 2015 Posts: 3332 Location: Canada Re: What is the length of the sides of a given cube? [#permalink] ### Show Tags 23 Aug 2018, 07:30 Top Contributor MathRevolution wrote: [Math Revolution GMAT math practice question] What is the length of the sides of a given cube? 1) The surface area of the cube is $$150$$ 2) The volume of the cube is $$125$$ IMPORTANT: For geometry Data Sufficiency questions, we are typically checking to see whether the statements "lock" a particular angle, length, or shape into having just one possible measurement. This concept is discussed in much greater detail in the video below This technique can save a lot of time. Target question: What is the length of the sides of a given cube? Statement 1: The surface area of the cube is 150 There are infinitely many cubes. Each cube has different surface area. So, we COULD go to our workshop and start making millions and millions of cubes of different sizes. Once we make a cube, we measure its surface area. We keep doing this until we find the ONE cube that has a surface area of 150. When we eventually find that cube, we COULD measure its side length (which is what the target question is asking for) Since there is only 1 cube in the universe that has a surface area of 150, then statement 1 must LOCK us in to exactly one shape. Therefore, statement 1 is SUFFICIENT Statement 2: The volume of the cube is 125 We can use the same approach here, since each different cube has a different volume. Since there's only 1 cube in the universe with a volume of 125, then statement 2 must LOCK us in to exactly one shape. Therefore, statement 2 is SUFFICIENT Answer: D RELATED VIDEO FROM OUR COURSE _________________ Test confidently with gmatprepnow.com Senior Manager Joined: 07 Jul 2012 Posts: 377 Location: India Concentration: Finance, Accounting GPA: 3.5 Re: What is the length of the sides of a given cube? [#permalink] ### Show Tags 23 Aug 2018, 08:55 Let the length of side of a cube= a 1) 6$$a^2$$= 150. Value of 'a' can be found. 2) $$a^3$$= 125. Value of 'a' can be found. Answer: D. _________________ Kindly hit kudos if my post helps! Board of Directors Status: QA & VA Forum Moderator Joined: 11 Jun 2011 Posts: 4330 Location: India GPA: 3.5 WE: Business Development (Commercial Banking) What is the length of the sides of a given cube? [#permalink] ### Show Tags 23 Aug 2018, 09:52 MathRevolution wrote: [Math Revolution GMAT math practice question] What is the length of the sides of a given cube? 1) The surface area of the cube is $$150$$ 2) The volume of the cube is $$125$$ From Statement I $$6a^2 = 150$$ Possible from this statement alone. From Statement II $$a^3 = 125$$ Possible from this statement alone. Answer must be (D) Each statement alone is sufficient to answer the question. _________________ Thanks and Regards Abhishek.... PLEASE FOLLOW THE RULES FOR POSTING IN QA AND VA FORUM AND USE SEARCH FUNCTION BEFORE POSTING NEW QUESTIONS How to use Search Function in GMAT Club | Rules for Posting in QA forum | Writing Mathematical Formulas |Rules for Posting in VA forum | Request Expert's Reply ( VA Forum Only ) Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6815 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: What is the length of the sides of a given cube? [#permalink] ### Show Tags 26 Aug 2018, 17:20 => Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. Since a cube is uniquely determined by its side length, we have only one variable. So, we should consider each of the conditions on their own first. Condition 1) Let $$x$$ be the side-length of the cube. Then condition 1) tells us that $$6x^2 = 150$$. Solving this equation yields $$x = 5$$. Condition 1) is sufficient. Condition 2) Let $$x$$ be the side-length of the cube. Then condition 2) tells us that $$x^3 = 125$$. Solving this equation yields $$x = 5$$. Condition 2) is sufficient. Therefore, D is the answer. Answer: D If the original condition includes “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations” etc., one more equation is required to answer the question. If each of conditions 1) and 2) provide an additional equation, there is a 59% chance that D is the answer, a 38% chance that A or B is the answer, and a 3% chance that the answer is C or E. Thus, answer D (conditions 1) and 2), when applied separately, are sufficient to answer the question) is most likely, but there may be cases where the answer is A,B,C or E. _________________ 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$149 for 3 month Online Course"
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Re: What is the length of the sides of a given cube? &nbs [#permalink] 26 Aug 2018, 17:20
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# What is the length of the sides of a given cube?

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