Q:

Find the number of points of intersection

There are two lines $L_1$ and $L_2$, which contain $m$ and $n$ points respectively. If each of $m$ points of $L_1$ be joined to each of the $n$ points of $L_2$ by straight line terminated by the points, then excluding the given points, then the no of points of intersection ?

A:

Yes you are correct
$${m \choose 2}*{n \choose 2}$$
$\Rightarrow$
$$\frac{(mn)(m-1)(n-1)}{4}$$

