Abc daycare wants to build a fence to enclose a rectangular playground. the area of the playground is 930 square feet. the fence along three of the sides costs $5 per foot and the fence along the fourth side, which will be made of brick, costs $20 per foot. find the length of the brick fence that will minimize the cost of enclosing the playground. (round your answer to one decimal place.)
Accepted Solution
A:
xy = 940
and
Cost = 5(2x) + 5y + 10y (I chose y to be the side with brick). The cost equation simplifies to:
C = 10x + 15y
Replace y in the cost equation with 940/x:
C = 10x + 15(940/x)
C = 10x + 14100/x <---this is the equation you need to minimize.
C' = 10 - 14100/x^2
10 - 14100/x^2 = 0
14100/x^2 = 10
x^2 = 14100/10 = 1410
x = sqrt(1410) = 37.55
y = 25.03 <---this is the length of the brick fence.