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# If the length of each edge of a certain rectangular solid is an

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Manager
Joined: 10 Sep 2014
Posts: 70
If the length of each edge of a certain rectangular solid is an [#permalink]

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09 Feb 2015, 03:36
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If the length of each edge of a certain rectangular solid is an integer and exactly four of its faces have the same dimensions, then what is the volume of the rectangular solid?

(1) Two of the faces have areas of 32 square units and 16 square units.

(2) One of the edges is twice the length of another edge.
[Reveal] Spoiler: OA

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Re: If the length of each edge of a certain rectangular solid is an [#permalink]

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09 Feb 2015, 12:56
Hi TARGET730,

This DS question has a number of interesting "restrictions" to it (and you have to pay careful attention to the restrictions to get the correct answer).

Here, we have a rectangular solid that has 4 faces with the same dimensions. In real basic terms, we have a box (NOT a cube), with the dimensions X, X and Y. We're also told that each dimension is an INTEGER. We're asked for the VOLUME of the solid.

Volume = (length)(width)(height)

Fact 1: Two of the faces have areas of 32 and 16

Since this rectangular solid has 4 faces with the same dimensions, the other 2 faces will have dimensions that match (but are different from the other 4 faces).

With the above values, we have just 2 possibilities:
The 4 sides are 32s and the 2 sides are 16s
The 4 sides are 16s and the 2 sides are 32s

While many Test Takers might dismiss this as insufficient, we need to do a bit more work to PROVE whether it's sufficient or insufficient.

If the 2 sides are 16s, then the two dimensions are 4 and 4
Since the others sides are 32s, those dimensions are 4 and 8
The volume of this solid is (4)(4)(8) = 126

If the 2 sides are 32s, then the two dimensions are (root32) and (root32).
The prompt stated that the dimensions had to be INTEGERS though, so this set of dimensions does NOT MATCH the restrictions given. Thus, there is only one answer in Fact 1.
Fact 1 is SUFFICIENT

Fact 2: One of the edges is twice the length of another.

We could have (4)(4)(8) =126
We could have (1)(1)(2) = 2
Fact 2 is INSUFFICIENT.

[Reveal] Spoiler:
A

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# Rich Cohen

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Special Offer: Save $75 + GMAT Club Tests Free Official GMAT Exam Packs + 70 Pt. Improvement Guarantee www.empowergmat.com/ ***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*********************** Manager Joined: 10 Sep 2014 Posts: 70 Re: If the length of each edge of a certain rectangular solid is an [#permalink] ### Show Tags 16 Feb 2015, 04:46 Hi Rich, I am not sure the OA is correct. i am trying to find the correct answer answer here. Can we consider the following possibilities with different volumes? Area 32 ------ 32 * 1 16 * 2 8 * 4 Area 16 ------ 1 * 16 2 * 8 4 * 4 Volume ------- 36 * 1 * 16 = 576 16 * 2 * 8 = 196 8 * 4 * 4 = 128 _________________ Press KUDOs if you find my explanation helpful EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 11633 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: 340 Q170 V170 Re: If the length of each edge of a certain rectangular solid is an [#permalink] ### Show Tags 16 Feb 2015, 17:52 Hi TARGET730, In the description of the rectangular solid, we're told that "4 of the faces have the same dimensions" - the ONLY way for that to occur is if the dimensions of the solid are X, X and Y (2 of the 3 dimensions MUST have the same length). We're also told that ALL the dimensions MUST be INTEGERS. Using these restrictions, how many of your 'examples' actually match? You'll find that just one "fits" (the 4x4x8), so the final answer is [Reveal] Spoiler: C GAMT assassins aren't born, they're made, Rich _________________ 760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com # Rich Cohen Co-Founder & GMAT Assassin Special Offer: Save$75 + GMAT Club Tests Free
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Re: If the length of each edge of a certain rectangular solid is an [#permalink]

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05 Sep 2017, 05:46
Ans is A
Length is integer, and 4 faces have equal areas
1) A1=32 and A2=16
from this LxB= 32 and $$B^2 = 16$$, $$=> B= 4$$ and $$L =8$$ and Volume= 8x4x4 = 128 cu.units

or BxL =32 and $$L^2 = 16$$, $$=> L=4$$ and$$B = 8$$ and in this case Volume = 4x4x8 = 128 cu. units

Note B and L cant take any other value as L is an integer mentioned in question.

2) $$L = 2B$$ or $$B = 2L$$
Clearly statement is insufficient to answer about volume which is $$L^2$$ x B or $$B^2$$ x L
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Re: If the length of each edge of a certain rectangular solid is an   [#permalink] 05 Sep 2017, 05:46
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