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rectangular solid inside cylinder

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by Uva@90 » Sat Aug 08, 2015 11:04 pm
A cylindrical tank has height of 10 feet and base with radius of 6 feet. if the thickness of the tank's sides is negligible , what is the volume , in cubic feet, of the largest rectangular solid that could be placed inside the tank?

A) 60
B) 360
C) 240 root (3)
D) 360 root (2)
E) 720

OA E
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Source: — Problem Solving |

by [email protected] » Sun Aug 09, 2015 9:12 am
Hi Uva@90,

I'm going to give you a couple of hints so that you can attempt this question again:

1) The largest rectangular solid that can be placed in a cylinder will have a SQUARE base.
2) Draw a picture of what you would see if you looked "down" into the cylinder (you'll see a circle with a square in it). The diagonal of the square will equal the diameter of the circle.

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by Uva@90 » Sun Aug 09, 2015 9:05 pm
[email protected] wrote:Hi Uva@90,

I'm going to give you a couple of hints so that you can attempt this question again:

1) The largest rectangular solid that can be placed in a cylinder will have a SQUARE base.
2) Draw a picture of what you would see if you looked "down" into the cylinder (you'll see a circle with a square in it). The diagonal of the square will equal the diameter of the circle.

GMAT assassins aren't born, they're made,
Rich
Hi Rich,

Using your info here is my shot,
Since Base is Square Each side would be 6root(2)(since diagonal = diameter=12 )

so volume = 6root(2) * 6roo(2) * 10 = 720

Is my approach correct ?

Thanks,
Regards,
Uva
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by nikhilgmat31 » Mon Aug 10, 2015 4:37 am
Am I correct to say

For a given Area

Square has the maximum Area with minimum Perimeter.

Rectangle has the maximum Perimeter with minimum Area.

Please suggest.

lets say a area of 4 sqcm.

side of square = 2
Perimeter = 4 * 2 = 8

side of rectangle can be = 2 & 2 with Perimeter = 2(2 + 2) = 8

side of rectangle can be = 4 & 1 with Perimeter = 2(4 + 1) = 10
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by DavidG@VeritasPrep » Mon Aug 10, 2015 4:44 am
Am I correct to say

For a given Area

Square has the maximum Area with minimum Perimeter.

Rectangle has the maximum Perimeter with minimum Area.

Please suggest.

lets say a area of 4 sqcm.

side of square = 2
Perimeter = 4 * 2 = 8

side of rectangle can be = 2 & 2 with Perimeter = 2(2 + 2) = 8

side of rectangle can be = 4 & 1 with Perimeter = 2(4 + 1) = 10
It is true that for a fixed perimeter, the rectangle that maximizes the area would be a square. (And remember that all squares are, in fact, rectangles.)
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by DavidG@VeritasPrep » Mon Aug 10, 2015 4:53 am
Am I correct to say

For a given Area

Square has the maximum Area with minimum Perimeter.

Rectangle has the maximum Perimeter with minimum Area.

Please suggest.

lets say a area of 4 sqcm.

side of square = 2
Perimeter = 4 * 2 = 8

side of rectangle can be = 2 & 2 with Perimeter = 2(2 + 2) = 8

side of rectangle can be = 4 & 1 with Perimeter = 2(4 + 1) = 10
Similarly, if you had two rectangles with equal area, one square and one non-square, the non-square would have the larger perimeter. (Which makes sense. If we took the non-square, kept the perimeter the same, and made it into a square, the area would then increase.)
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by [email protected] » Mon Aug 10, 2015 9:14 am
Hi Uva@90,

YES, you are correct. Nicely done.

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by Uva@90 » Mon Aug 10, 2015 7:16 pm
nikhilgmat31 wrote:Am I correct to say

For a given Area

Square has the maximum Area with minimum Perimeter.

Rectangle has the maximum Perimeter with minimum Area.

Please suggest.

lets say a area of 4 sqcm.

side of square = 2
Perimeter = 4 * 2 = 8

side of rectangle can be = 2 & 2 with Perimeter = 2(2 + 2) = 8

side of rectangle can be = 4 & 1 with Perimeter = 2(4 + 1) = 10
Nikhil,

Normally Regular polygon has the greater Area.

For Example Square > Rectangle
and Equilateral Triangle > any other Triangle.

Thanks.
Regards,
Uva.
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by nikhilgmat31 » Tue Aug 11, 2015 3:30 am
Thanks Uva it helps.

so a rectangle with a given perimeter has maximum area when it is a SQUARE. (Regular Polygon)


Similarly a regular polygon(or a square) with a given area has minimum perimeter when it is a rectangle.
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