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# A cube has a volume of 72. If it is divided into 8 equal cubes, the

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Joined: 02 Sep 2009
Posts: 43314

Kudos [?]: 139356 [0], given: 12786

A cube has a volume of 72. If it is divided into 8 equal cubes, the [#permalink]

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06 Dec 2017, 03:19
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A cube has a volume of 72. If it is divided into 8 equal cubes, the ratio of an edge of a smaller cube to an edge of the original cube is

(A) 1 : 2
(B) 1: 3
(C) 1 : 3√2
(D) 2 : 9
(E) 1 : 9
[Reveal] Spoiler: OA

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Kudos [?]: 139356 [0], given: 12786

Director
Joined: 18 Aug 2016
Posts: 627

Kudos [?]: 208 [0], given: 166

Concentration: Strategy, Technology
GMAT 1: 630 Q47 V29
GMAT 2: 740 Q51 V38
A cube has a volume of 72. If it is divided into 8 equal cubes, the [#permalink]

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06 Dec 2017, 03:42
Bunuel wrote:
A cube has a volume of 72. If it is divided into 8 equal cubes, the ratio of an edge of a smaller cube to an edge of the original cube is

(A) 1 : 2
(B) 1: 3
(C) 1 : 3√2
(D) 2 : 9
(E) 1 : 9

Volume of each small cube = 72/8 = 9
Edge of each small cube = 9^1/3
Edge of Original cube = 72^1/3
$$(9^(1/3)) / (8^(1/3)) * (9^(1/3))$$
1/2
A
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Luckisnoexcuse

Kudos [?]: 208 [0], given: 166

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Joined: 11 Sep 2015
Posts: 1983

Kudos [?]: 2864 [0], given: 364

Re: A cube has a volume of 72. If it is divided into 8 equal cubes, the [#permalink]

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06 Dec 2017, 09:17
Expert's post
Top Contributor
Bunuel wrote:
A cube has a volume of 72. If it is divided into 8 equal cubes, the ratio of an edge of a smaller cube to an edge of the original cube is

(A) 1 : 2
(B) 1: 3
(C) 1 : 3√2
(D) 2 : 9
(E) 1 : 9

Great question!
The great thing about it is that the volume of the original cube is irrelevant.
It all comes down to what happens when we divide ANY cube into 8 equal cubes.
Here's what I mean.

Take a cube and divide it into 8 equal cubes...

If we let x = the length of one edge of the ORIGINAL cube....

....then x/2 = the length of one edge of the SMALLER cube....

What is the ratio of an edge of a smaller cube to an edge of the original cube?
Get get: x/2 : x
Divide both sides by x to get the EQUIVALENT ratio: 1/2 : 1
Multiply both sides by 2 to get the EQUIVALENT ratio: 1 : 2

Cheers,
Brent
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Kudos [?]: 2864 [0], given: 364

Re: A cube has a volume of 72. If it is divided into 8 equal cubes, the   [#permalink] 06 Dec 2017, 09:17
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