A hollow spherical metallic ball has an external diameter 6 cm and is 1/2 cm thick. The volume of metal used in the ball is :

Answer: Option D

External radius = 3 cm
Internal radius = (3 - 0.5) cm = 2.5 cm
Volume of the metal :
$$\begin{array}{rl}& =\left[\frac{4}{3}\times \frac{22}{7}\times \left\{{\left(3\right)}^3-{\left(2.5\right)}^3\right\}\right]\text{ c}{\text{m}}^3\\ & =\left(\frac{4}{3}\times \frac{22}{7}\times \frac{91}{8}\right)\text{ c}{\text{m}}^3\\ & =\left(\frac{143}{3}\right)\text{ c}{\text{m}}^3\\ & =47\frac{2}{3}\text{ c}{\text{m}}^3\end{array}$$