algebra 1
posted by casey .
Blue prints allow an area of 20,000 square feet for the playground. the width of the rectangular playground is 80 feet less than its length and its perimeter is 640 freet. what is the length of the playground?

Let L = length
W = L80
So L80 + L80 + L + L = 640.
Solve for L. 
Area = L * W
Perimeter = 2L + 2W
W = L  80
So, plug in the width formula into the perimeter equation, which would look like this:
640 = 2L + 2(L80)
640 = 2L + 2L  160
640 = 4L  160
800 = 4L
L = 200
It looks like you don't even need the information about the area of the playground; just the perimeter.
Hope this helps! If you have any questions about my method just post :)