A water tank is 30 m long, 20 m wide and 12 m deep. It is made of iron sheet which is 3 m wide. The tank is closed at the top. If the cost of iron sheet is Rs. 10 per meter, then what is the total cost of iron sheet required to build the tank?

8000

Dimension of water tank is 30m×20m×12m

T.S.A. of tank = 2 [lb + bh + hl]

                    = 2 [(30×20) + (20×12) + (12×30)]

                    = 2[600 + 240 + 360]

                    = 2 × 1200 = 2400 m²

Area of sheet = 2400 m²

∴ l × b = 2400 ⇒ l × 3 = 2400 ⇒ l = 800 m

Cost of sheet = Rs.(800×10) = Rs. 8000