The internal radius and thickness of a hollow hemisphere are 5 cm and 3 cm respectively. Find its total surface area.

Let r and w be the internal radius and thickness of a hollow hemisphere respectively.
The external radius of the hollow hemisphere, R = w + r = 5 + 3 = 8 cm
r = 5 cm and R = 8 cm.
Now, the Total surface area of the hollow hemisphere,

$\begin{array}{rcl}\mathrm{Total} \mathrm{surface} \mathrm{area}& =& \mathrm{\pi }\left(3{\mathrm{R}}^2+{\mathrm{r}}^2\right)\end{array}$

$\begin{array}{rcl} & =& \frac{22}{7}\times (3\times 8^2+5^2)\end{array}$

$\begin{array}{rcl} & =& \frac{22}{7}\times \left(217\right)\end{array}$

$\begin{array}{rcl} & =& 682 {\mathrm{cm}}^2\end{array}$

Therefore the total surface area of the hollow hemisphere will be 682 cm².