Posted by alex on Monday, October 5, 2009 at 4:33pm.
faye has 20 feet of fencing to make a rectangular pen for her dog.What is the largest area she can fence in?

math  alex, Monday, October 5, 2009 at 4:34pm
20 feet

math  alex, Monday, October 5, 2009 at 4:38pm
is that right im just gessing

math  Ms. Sue, Monday, October 5, 2009 at 4:39pm
Let's see 
it could be 5 + 5 + 5 + 5
or 4 + 4 + 6 + 6
or 3 + 3 + 7 + 7
Find the areas of these pens.
A = length times width
So  a 3 foot by 7 foot pen would be 21 square feet.
Find the areas of the other two pens. Which gives you the most square feet?

math  MathMate, Monday, October 5, 2009 at 4:39pm
For a math question:
Make a table of width (W) and lengths (L) that add up to 20 for perimeter = 2(W+L).
Calculate the area for each line. Choose the biggest area.
Width Length Area
1 9 9
2 8 16
3 7 21
4 6 24
.....
8 2 16
9 1 9
For a calculus question:
Let W=width, then
(10W)=length, and
Area=A(W)=W(10W)=10WW²
For maximum or minimum:
dA/dW=102W=0, or W=5
d²A/dW²=2 <0 so maximum.
A(5)=5(105)=25 (maximum area)

math  alex, Monday, October 5, 2009 at 5:15pm
hi im only in 4th grade so i really kind of need simple answers

math  Ms. Sue, Monday, October 5, 2009 at 5:27pm
Please see my answer. I'm sure you can figure out your answer using that information.

math  alex, Monday, October 5, 2009 at 5:28pm
thanks ms.sue u rock

math  Ms. Sue, Monday, October 5, 2009 at 5:30pm
You're welcome, Alex. :)
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