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

The tank is a closed cuboid.

Length $l = 30\text{ m}$, Width $b = 20\text{ m}$, Height $h = 12\text{ m}$

Surface area of a closed cuboid:

$2(lb + bh + hl)$

$= 2(30 \times 20 + 20 \times 12 + 30 \times 12)$

$= 2(600 + 240 + 360)$

$= 2 \times 1200 = 2400\text{ m}^2$

The iron sheet is 3 m wide.

$\text{Length of sheet} = \frac{\text{Area}}{\text{Width}} = \frac{2400}{3} = 800\text{ m}$

Cost = ₹10 per meter (of 3 m wide sheet)

$800 \times 10 = \text{₹8000}$