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Geometry problem

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by The Jock » Tue Jun 29, 2010 3:34 am
A cube has sides measuring 6 inches. What is the greatest possible (straight-line) distance, in inches, between any
two points on the box?
(A) 2underroot6
(B) 3underroot6
(C) 6underroot2
(D) 6underroot3
(E) 12

Not getting the exact picture how to get the answer. Please help
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Source: — Problem Solving |

by nathanalgren » Tue Jun 29, 2010 4:22 am
I guess it is 6 squareroot3. Imagine you draw a line from the left bottom corner of a cube to right top corner of it. And try to calculate it.
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by saurabhmahajan » Tue Jun 29, 2010 5:38 am
me too answer is 6root3.

see the attachment.
first find length for side AC (red line)
then for side AD (blue line)
since AD is longest line the ans is 6 root 3
Attachments
Cube.JPG
Thanks and regards,
Saurabh Mahajan

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by GMATGuruNY » Tue Jun 29, 2010 6:03 am
The Jock wrote:A cube has sides measuring 6 inches. What is the greatest possible (straight-line) distance, in inches, between any
two points on the box?
(A) 2underroot6
(B) 3underroot6
(C) 6underroot2
(D) 6underroot3
(E) 12

Not getting the exact picture how to get the answer. Please help
The greatest possible line that be drawn in a box is called the main diagonal.

If l = length, w = width, h = height, and d = main diagonal, then use the super-pythagorean theorem:

l^2 + w^2 + h^2 = d^2

In a cube, the length, width and height are the same, so if e = edge:

3(e^2) = d^2

In the problem above, e = 6, so:

3(6^2) = d^2
3(36) = d^2
108=d^2
d = sqrt(108) = sqrt(36 * 3) = sqrt(36) * sqrt(3) = 6sqrt(3)

The correct answer is D.
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