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The useful life of a certain piece of equipment is determine

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The useful life of a certain piece of equipment is determine [#permalink] New post 20 Feb 2008, 14:00
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78% (02:06) correct 22% (00:38) wrong based on 26 sessions
The useful life of a certain piece of equipment is determined by the following formula: u =(8d)/h^2, where u is the useful life of the equipment, in years, d is the density of the underlying material, in g/cm3, and h is the number of hours of daily usage of the equipment. If the density of the underlying material is doubled and the daily usage of the equipment is halved, what will be the percentage increase in the useful life of the equipment?

A. 300%
B. 400%
C. 600%
D. 700%
E. 800%

OPEN DISCUSSION OF THIS QUESTION IS HERE: the-useful-life-of-a-certain-piece-of-equipment-is-determine-101496.html
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Last edited by Bunuel on 27 Oct 2013, 04:21, edited 1 time in total.
Renamed the topic, edited the question, added the OA and moved to PS forum.
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Re: MGMAT - Formula [#permalink] New post 20 Feb 2008, 14:09
bmwhype2 wrote:
The useful life of a certain piece of equipment is determined by the following formula: u =(8d)/h2, where u is the useful life of the equipment, in years, d is the density of the underlying material, in g/cm3, and h is the number of hours of daily usage of the equipment. If the density of the underlying material is doubled and the daily usage of the equipment is halved, what will be the percentage increase in the useful life of the equipment?

300%
400%
600%
700%
800%


if it's h^2 then D is the answer
I really don't like units though :)
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Re: MGMAT - Formula [#permalink] New post 20 Feb 2008, 14:09
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bmwhype2 wrote:
The useful life of a certain piece of equipment is determined by the following formula: u =(8d)/h2, where u is the useful life of the equipment, in years, d is the density of the underlying material, in g/cm3, and h is the number of hours of daily usage of the equipment. If the density of the underlying material is doubled and the daily usage of the equipment is halved, what will be the percentage increase in the useful life of the equipment?

300%
400%
600%
700%
800%


I am assuming your question is u =(8d)/h^2,

Hence new equation would be
\(u_1 = \frac{8 * (2d)}{(\frac{h}{2})^2}\) --> \(u_1 = 8 * \frac{8 * d} {({h})^2}\) --> \(u_1 = 8*u\)

Hence 700% increase....
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Re: MGMAT - Formula [#permalink] New post 20 Feb 2008, 18:01
agreed. assuming question is h^2, we have:

percentage change = u2-u1/u2 * 100

u1=8d/h^2

u2=[8*2d]/[(h/2)^2] -->64d/h^2

64d/h^2 - 8d/h^2 / 8d/h^2 = 7*100 = 700%
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Re: MGMAT - Formula [#permalink] New post 21 Feb 2008, 01:42
U = (8d) / h2 without any percentage change
D = 1 h = 1
Uold = 4
With change
Unew = 16d / h
D = 1 h = 1
Unew = 16

400%
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Re: MGMAT - Formula [#permalink] New post 27 Oct 2013, 04:17
hanumayamma wrote:
U = (8d) / h2 without any percentage change
D = 1 h = 1
Uold = 4
With change
Unew = 16d / h
D = 1 h = 1
Unew = 16

400%



Forgot to divide last h by 2 and then squared
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Re: The useful life of a certain piece of equipment is determine [#permalink] New post 27 Oct 2013, 04:23
Expert's post
Re: The useful life of a certain piece of equipment is determine   [#permalink] 27 Oct 2013, 04:23
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