Last visit was: 11 Dec 2024, 03:47 It is currently 11 Dec 2024, 03:47
Close
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Close
Request Expert Reply
Confirm Cancel
User avatar
Brainless
Joined: 25 Jun 2003
Last visit: 12 Mar 2005
Posts: 54
Own Kudos:
Posts: 54
Kudos: 5
Kudos
Add Kudos
Bookmarks
Bookmark this Post
User avatar
brstorewala
Joined: 28 Feb 2003
Last visit: 02 May 2004
Posts: 50
Own Kudos:
Posts: 50
Kudos: 33
Kudos
Add Kudos
Bookmarks
Bookmark this Post
avatar
stolyar
Joined: 03 Feb 2003
Last visit: 06 May 2014
Posts: 1,012
Own Kudos:
Posts: 1,012
Kudos: 1,751
Kudos
Add Kudos
Bookmarks
Bookmark this Post
User avatar
Brainless
Joined: 25 Jun 2003
Last visit: 12 Mar 2005
Posts: 54
Own Kudos:
Posts: 54
Kudos: 5
Kudos
Add Kudos
Bookmarks
Bookmark this Post
stolyar
No problem, Sir

You have to bend your metal sheet in some way, to have a П-shaped object. Since, the lenght is not important, concentrate on a П-section.
A section of maximal area will give you maximal volume.

So, how to bend a 12' line in 3-side, П-object to cover the maximal area?
Imagine a rectangular with sides: X, X, 12тАУ2X, 12тАУ2X. Let X be a vertical side, and 12тАУ2X be a horizontal one.

X+X+12тАУ2X=given 12 and one side is virtual

An area of the section is X*(12тАУ2X)= 12XтАУ2X^2
A derivative is 12тАУ4X=0, where X=3

so your gutter should have two 3' vertical sides and one 6' horizontal.
Such section gives you 18 square inch area

All others are smaller (10+1+1) gives 10
(8+2+2) gives 16
(4+4+4) gives 16

With the same perimetr a circle has the smallest area, but a square -- the greatest.


Gotcha, So I all I need to do is find the maximum value for the qudratic function representing the area of П-section.
User avatar
Brainless
Joined: 25 Jun 2003
Last visit: 12 Mar 2005
Posts: 54
Own Kudos:
Posts: 54
Kudos: 5
Kudos
Add Kudos
Bookmarks
Bookmark this Post
brstorewala
try out the combinations

2*5 =10
4*4 =16
5*3.5 =17.5
6*3 = 18
7*2.5 = 17.5
8*2 =16


maximum is at 18, so it should be turned up 3"


Excellent idea to minimize the time in actual test !! Agreed
User avatar
kpadma
Joined: 03 Jul 2003
Last visit: 20 Oct 2004
Posts: 380
Own Kudos:
Posts: 380
Kudos: 501
Kudos
Add Kudos
Bookmarks
Bookmark this Post
stolyar
No problem, Sir

You have to bend your metal sheet in some way, to have a П-shaped object. Since, the lenght is not important, concentrate on a П-section.
A section of maximal area will give you maximal volume.

So, how to bend a 12' line in 3-side, П-object to cover the maximal area?
Imagine a rectangular with sides: X, X, 12тАУ2X, 12тАУ2X. Let X be a vertical side, and 12тАУ2X be a horizontal one.

X+X+12тАУ2X=given 12 and one side is virtual

An area of the section is X*(12тАУ2X)= 12XтАУ2X^2
A derivative is 12тАУ4X=0, where X=3

so your gutter should have two 3' vertical sides and one 6' horizontal.
Such section gives you 18 square inch area

All others are smaller (10+1+1) gives 10
(8+2+2) gives 16
(4+4+4) gives 16

With the same perimetr a circle has the smallest area, but a square -- the greatest.


An area of the section is X*(12тАУ2X)= 12XтАУ2X^2
A derivative is 12тАУ4X=0, where X=3

This does not look correct!
User avatar
Brainless
Joined: 25 Jun 2003
Last visit: 12 Mar 2005
Posts: 54
Own Kudos:
Posts: 54
Kudos: 5
Kudos
Add Kudos
Bookmarks
Bookmark this Post
kpadma
stolyar
No problem, Sir

You have to bend your metal sheet in some way, to have a П-shaped object. Since, the lenght is not important, concentrate on a П-section.
A section of maximal area will give you maximal volume.

So, how to bend a 12' line in 3-side, П-object to cover the maximal area?
Imagine a rectangular with sides: X, X, 12тАУ2X, 12тАУ2X. Let X be a vertical side, and 12тАУ2X be a horizontal one.

X+X+12тАУ2X=given 12 and one side is virtual

An area of the section is X*(12тАУ2X)= 12XтАУ2X^2
A derivative is 12тАУ4X=0, where X=3

so your gutter should have two 3' vertical sides and one 6' horizontal.
Such section gives you 18 square inch area

All others are smaller (10+1+1) gives 10
(8+2+2) gives 16
(4+4+4) gives 16

With the same perimetr a circle has the smallest area, but a square -- the greatest.

An area of the section is X*(12тАУ2X)= 12XтАУ2X^2
A derivative is 12тАУ4X=0, where X=3

This does not look correct!


Brush up your calculus basics !! ( GMAT does not test u in calculus)

d (12x-x^2)
---- = 12-4x, right ?
dx

maximum value is 3 as you see from the solution
User avatar
kpadma
Joined: 03 Jul 2003
Last visit: 20 Oct 2004
Posts: 380
Own Kudos:
Posts: 380
Kudos: 501
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Thanks!
:oops:



Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
Moderator:
Senior Moderator - Masters Forum
3116 posts