Question

A cubical water tank holds $125$ litres of water. What will be the cost of whitewashing its outer walls, if the rate is $\$10/$ cm${}^2$ ?

Answer 1

Amount of water in the tank = Volume of the tank

We know, $1$ litre $=1000$ cm${}^3$
$\therefore 125$ litre $=125\times 1000=125000$ cm${}^3$

Thus, volume of the tank $=s^3=125000$ cm${}^3$, where $s$ is the side of the tank
$⟹s=\sqrt[3]{3125000}=50$ cm

Whitewashing will be done on the outer walls of the tank, which means the area that will be covered is the lateral surface area of the cuboidal tank.

Lateral Surface Area of the tank $=4\times s^2=4\times {50}^2=4\times 2500=10,000$ cm${}^2$

Rate of painting $=\$10/$cm${}^2$
$\therefore$ Cost of whitewashing the tank $10\times 10000=\$100,000$