Posted by Khelany on Friday, September 6, 2013 at 11:31pm.
A rectangular rice land is to be fenced along 4 sides and in the middle to divide it into to 2 equal areas. If 200m of fencing is available, what is the maximum area to be fenced?

Math  Graham, Friday, September 6, 2013 at 11:50pm
Assume that length l is greater than or equal to width w. Assert that the dividing fencing must be equal to the width (ie it must be perpendicular) by reasoning that if it were at any other angle, it would be longer, and the length would be reduced.
A = w * l
200 = 3w + 2l
.: A = w*(2003w)/2
or A = 100 w  (3/2) w^2
Take the derivative and find when this is 0.
0 = (d/dw) (100 w(3/2)w^2)
Solve for w, use to determine A 
Math  Anonymous, Sunday, September 8, 2013 at 10:11am
where did you get the 3w

Math  Graham, Tuesday, October 1, 2013 at 3:21am
The 200m fencing is used for two lengthsides (l), two widthsides (w) and the middle divider (w).
This: 200 = 2l + 3w