A tank 20 m long, 12 m wide and 8 m deep is to be made of iron sheet. It is open at the top. Determine the cost of iron-sheet, at the rate of ₹ 12.50 per metre, if the sheet is 2.5 m wide.

Given:

Dimensions of the tank = 20 m x 12 m x 8 m

Width of the iron sheet = 2.5 m

Rate of iron sheet = ₹ 12.50 per metre

Area of sheet = Surface area of the tank

⇒ Length_sheet x Width_sheet = Area of 4 walls of the tank + Area of base

⇒ Length_sheet x 2.5 m = 2(l + b)h + l x b

⇒ Length_sheet x 2.5 m = 2(20 + 12)8 + 20 x 12 m²

⇒ Length_sheet x 2.5 m = 2 x 32 x 8 + 240 m²

⇒ Length_sheet x 2.5 m = 512 + 240 m²

⇒ Length_sheet x 2.5 m = 752 m²

⇒ Length_sheet = $\dfrac{752}{2.5}$ m

⇒ Length_sheet = 300.8 m

Cost of the sheet = Length of the sheet x Rate of iron sheet

= 300.8 x 12.50

= ₹ 3,760

Hence, the total cost of the iron sheet is ₹ 3,760.