Geometry 4 : GMAT Problem Solving (PS)

Geometry 4

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Geometry 4 [#permalink]

26 Sep 2009, 03:23

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Q.
If V is the volume of a cuboid of dimension x, y, z and A is its surface, then A/V will be equal to
1. x^2*y^2*z^2
2. ½( 1/xy + 1/ xz + 1/ yz)
3. ½ ( 1/x +1/y+1/z)

OA- 3

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Re: Geometry 4 [#permalink]

26 Sep 2009, 06:34

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Volume of it is equal to V= x*y*z
Area of it is equal to the sum of 6 regions on its surface. There are 2 surfaces with dimensions x and y, two with x and z and two with y and z.
So the area = A= 2*x*y+2*x*z+2*y*z
A/V= 2(xy+xz+yz)/xyz= 2(1/x+1/y+1/z).
It is like option c but not the same. Please control OA

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Re: Geometry 4 [#permalink]

26 Sep 2009, 07:44

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virtualanimosity wrote:

Q.
If V is the volume of a cuboid of dimension x, y, z and A is its surface, then A/V will be equal to
1. x^2*y^2*z^2
2. ½( 1/xy + 1/ xz + 1/ yz)
3. ½ ( 1/x +1/y+1/z)

OA- 3

V = xyz
A = 2 (xy + yz + zx)

A/V= 2(xy+yz+zx) / xyz = 2(1/x + 1/y + 1/z)

If question were what is V/A, then
V/A = xyz / [2(xy+yz+zx)] = 1 / [2 (1/x + 1/y + 1/z)]

In the given answer choices, if u put a extra bracket in the answer choice 3, then that will match with V/A.
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Re: Geometry 4 [#permalink]

26 Sep 2009, 11:21

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Area = 2xy + 2yz + 2xz
Volume = xyz
Thus A/V = 2((xy + yz + xz)/xyz)
which is the same as
A/V = 2(1/x + 1/y + 1/z)

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Re: Geometry 4 [#permalink]

26 Sep 2009, 11:31

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area = 2(xy+yz+xz)
volume = xyz

A/V = 2(xy+yz+xz) / xyz = 2 (1/x+1/y+1/z)
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Re: Geometry 4 [#permalink]

13 Oct 2009, 23:25

virtualanimosity wrote:

Q.
If V is the volume of a cuboid of dimension x, y, z and A is its surface, then A/V will be equal to
1. x^2*y^2*z^2
2. ½( 1/xy + 1/ xz + 1/ yz)
3. ½ ( 1/x +1/y+1/z)

OA- 3

OA cannot be 3. A/V will be 2( 1/x +1/y+1/z)

What is the source of this question?

Re: Geometry 4 [#permalink] 13 Oct 2009, 23:25

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Geometry 4

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