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If the length of each edge in a cube is increased by the

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SVP
Joined: 30 Apr 2008
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If the length of each edge in a cube is increased by the [#permalink]

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18 Nov 2008, 09:03
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If the length of each edge in a cube is increased by the same percent and the result was that the cube had 25% more volume than it originally had, by what percentage were the edges increased?
(A) $$\sqrt[3]{25%}$$
(B) 5%
(C) 7.7%
(D) 8.33%
(E) 12.5%
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J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$. GMAT Club Premium Membership - big benefits and savings Kudos [?]: 615 [0], given: 32 SVP Joined: 30 Apr 2008 Posts: 1868 Kudos [?]: 615 [0], given: 32 Location: Oklahoma City Schools: Hard Knocks Re: Increase in volume of Cube [#permalink] Show Tags 18 Nov 2008, 09:27 can you show your work? (i.e., how did you get that answer?) spiridon wrote: C 7.7% _________________ ------------------------------------ J Allen Morris **I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.

GMAT Club Premium Membership - big benefits and savings

Kudos [?]: 615 [0], given: 32

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Re: Increase in volume of Cube [#permalink]

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18 Nov 2008, 09:33
used plug ins (deduction)

figured would be easier then to try algebraic solution so..

original cube 10x10x10=1000 volume
increased side by (pick C) 10*1.077=10.77
10.77*10.77*10.77=1250 volume

compare volumes and get 25% increase

is that right?
_________________

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Kudos [?]: 37 [0], given: 1

SVP
Joined: 30 Apr 2008
Posts: 1868

Kudos [?]: 615 [0], given: 32

Location: Oklahoma City
Schools: Hard Knocks
Re: Increase in volume of Cube [#permalink]

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18 Nov 2008, 09:38
I think it's right. I did use number picking too.

I used volume of the original cube is 8 (because it's a cube of 2) and increase that by 25% gives us a new volume of 10.

To find one side of the larger cube, it's the cube root of 10 divided by 2 because 2 was the original length of one side of the cube.

$$\sqrt[3]{10}/2 = 1.077$$, because the question asks for the amount of increase, we subtract 1 from this value and get .077, or 7.7%. I don't have the OA, but it seems to be right to me. We each used different numbers and came up with the same answer. Most likely true.

spiridon wrote:
used plug ins (deduction)

figured would be easier then to try algebraic solution so..

original cube 10x10x10=1000 volume
increased side by (pick C) 10*1.077=10.77
10.77*10.77*10.77=1250 volume

compare volumes and get 25% increase

is that right?

_________________

------------------------------------
J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a.

GMAT Club Premium Membership - big benefits and savings

Kudos [?]: 615 [0], given: 32

Re: Increase in volume of Cube   [#permalink] 18 Nov 2008, 09:38
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