$(1)$ In $\Delta ABC$,$AD$ is an altitude. If $BC = 8 \text{ cm}$ and $AD = 5 \text{ cm}$,then $\text{ar}(\Delta ABC) = \dots \text{ cm}^2$.
$(2)$ $A$ $\dots$ of a triangle divides the triangle into two triangles of equal area.

(A) $(1)$ The area of a triangle is given by the formula $\text{ar}(\Delta ABC) = \frac{1}{2} \times \text{base} \times \text{height}$.
Given $\text{base} (BC) = 8 \text{ cm}$ and $\text{height} (AD) = 5 \text{ cm}$.
$\text{ar}(\Delta ABC) = \frac{1}{2} \times 8 \times 5 = 20 \text{ cm}^2$.
$(2)$ $A$ median of a triangle divides the triangle into two triangles of equal area.