My Math Forum  

Go Back   My Math Forum > High School Math Forum > Algebra

Algebra Pre-Algebra and Basic Algebra Math Forum


Reply
 
LinkBack Thread Tools Display Modes
November 1st, 2011, 01:26 PM   #1
Newbie
 
Joined: Nov 2011

Posts: 4
Thanks: 0

Finding the width of a uniform border

A mural is to be painted on a wall that is 15 units long and 12 units high. A border of uniform width is to surround the mural. If the mural is to cover 75% of the area of the wall, how wide must the border be?
tmac20 is offline  
 
November 1st, 2011, 01:32 PM   #2
Global Moderator
 
The Chaz's Avatar
 
Joined: Nov 2009
From: Northwest Arkansas

Posts: 2,767
Thanks: 5

Re: Finding the width of a uniform border

The "75%..." part is the easiest to tackle.

The wall has area 12 x 15 = 180 (square units), so we want our mural to have area .75*180 = 135 (square units).

Now we determine the dimensions of the mural.

The requirement of a "uniform border" means that the mural will have dimensions (15 - 2x)*(12 - 2x), where x is the width of the border.
^ deducing this is often the hardest part of problems like this, so draw a picture and see why my claim is true.

So (15 - 2x)*(12 - 2x) = 135 is the equation for the area of the mural.

FOIL, get in standard form, then factor/quadratic formula.
The Chaz is offline  
November 1st, 2011, 01:33 PM   #3
Senior Member
 
MarkFL's Avatar
 
Joined: Jul 2010
From: St. Augustine, FL., U.S.A.'s oldest city

Posts: 12,211
Thanks: 521

Math Focus: Calculus/ODEs
Re: Finding the width of a uniform border

Let W be the width and H be the height of the wall, and B be the width of the border. We then require:









Application of the quadratic formula yields:



Letting W = 15 m and H = 12 m, we find:



The only root that makes sense is
MarkFL is offline  
November 1st, 2011, 03:57 PM   #4
Newbie
 
Joined: Nov 2011

Posts: 1
Thanks: 0

Re: Finding the width of a uniform border

ZOMG you don't know? so nooby
CuhCalvin is offline  
Reply

  My Math Forum > High School Math Forum > Algebra

Tags
border, finding, uniform, width



Search tags for this page
Click on a term to search for related topics.
Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Border Question - Urgent helpmeplease12 Algebra 2 January 27th, 2014 01:18 PM
Finding minimal width of polygon inkexit Algebra 1 April 29th, 2012 09:04 AM
calculate width and height clankill3r Algebra 5 January 2nd, 2012 08:34 AM
find a point on the border of a rectangle. mvrijswijk Algebra 5 November 10th, 2011 01:13 PM
Calculating Width & Height of a rectange...? atw Algebra 6 May 18th, 2007 06:20 AM





Copyright © 2019 My Math Forum. All rights reserved.