math
posted by alex .
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
20 feet

math 
alex
is that right im just gessing

math 
Ms. Sue
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
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
hi im only in 4th grade so i really kind of need simple answers

math 
Ms. Sue
Please see my answer. I'm sure you can figure out your answer using that information.

math 
alex
thanks ms.sue u rock

math 
Ms. Sue
You're welcome, Alex. :)
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