A closed box is a cuboid in shape with length = 40 cm, breadth = 30 cm and height = 50 cm. It is made of thin metal sheet. Find the cost of metal sheets required to make 20 such boxes, if 1 m² of metal sheet costs ₹ 45.

Given:

The length of the closed box = 40 cm = 0.4 m.

The breadth of the closed box = 30 cm = 0.3 m.

The height of the closed box = 50 cm = 0.5 m.

As we know, the total surface area of the cuboid = 2(l x b + b x h + h x l)

= 2(0.4 x 0.3 + 0.3 x 0.5 + 0.5 x 0.4) m²

= 2(0.12 + 0.15 + 0.2) m²

= 2 x 0.47 m²

= 0.94 m²

Total surface area of 20 boxes = Surface area of 1 box $\times$ 20

= 0.94 x 20 m²

= 18.8 m²

Cost of 1 m² sheet = ₹ 45

Total cost = Total surface area x Cost of 1 m² sheet

= ₹ 18.8 x 45

= ₹ 846

Hence, the total cost of the sheet is ₹ 846.