A storage shed is to be built in the shape of a box with a square base. It is to have a volume of 250 cubic feet. The concrete for the base costs ​$4 per square​ foot, the material for the roof costs ​$6 per square​ foot, and the material for the sides costs ​$2.50 per square foot. Find the dimensions of the most economical shed.

Respuesta :

Answer:

the dimensions of the most economical shed are height = 10 ft and side 5 ft

Step-by-step explanation:

Given data

volume = 250 cubic feet

base costs = $4 per square​ foot

material for the roof costs =  ​$6 per square​ foot

material for the sides costs = ​$2.50 per square foot

to find out

the dimensions of the most economical shed

solution

let us consider length of side x and height is h

so we can say x²h = 250

and h = 250 / x²

now cost of material  = cost of base + cost top + cost 4 side

cost  = x²(4) + x²(6)  + 4xh (2.5)

cost = 10  x² + 10xh

put here h = 250 / x²

cost = 10  x² + 10x (250/ x² )

cost = 10  x² +  (2500/ x )

differentiate and  we get

c' = 20 x - 2500 / x²

put c' = 0 solve x

20 x - 2500 / x²  = 0

x = 5

so we say one side is 5 ft  base

and height is  h = 250 / x²

h = 250 / 5²

height = 10 ft

This is about Optimization in Mathematics.

Length of base = 5 ft

Width of base  = 5 ft

Height of box = 10 ft

  • Let the length of the base be x
  • Let the height of box be y

  • We are given Volume = 250 ft³

Volume of a box is; V = length × width × height

Since the base is a square, then length = width = x

Thus;

V = x²y

x²y = 250

y = 250/x²

  • The base will have the same area with the roof.

Thus, cost of base = $4x²

Cost of roof = $6x²

Area of the side is xy and so cost of 4 sides = 4(2.5xy) = 10xy

  • Thus;

Total Cost; C =  4x² + 6x² + 10xy

C = 10x² + 10xy

Putting 250/x² for y, we have;

C = 10x² + 2500/x

  • The dimension for the most economical cost will occur when dC/dx = 0

Thus;

dC/dx = 20x - 2500/x²

At dC/dx = 0;

20x - 2500/x² = 0

20x = 2500/x²

x³ = 2500/20

x³ = 125

x = ∛125

x = 5 ft

  • Putting 5 for x in y = 250/x²;

y = 250/5²

y = 250/25

y = 10 ft

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