IMO Shortlist 1968 problem 24
Dodao/la:
arhiva2. travnja 2012. Given
![k](/media/m/f/1/3/f135be660b73381aa6bec048f0f79afc.png)
parallel lines
![l_1, \ldots, l_k](/media/m/4/c/4/4c44e6be47d8150dbddffbcd7eab06d1.png)
and
![n_i](/media/m/e/c/f/ecf060a8faabbcf3c734f47bb5559433.png)
points on the line
![l_i, i = 1, 2, \ldots, k](/media/m/6/8/e/68e1789fa415fe0860f14cd17c2ae884.png)
, find the maximum possible number of triangles with vertices at these points.
%V0
Given $k$ parallel lines $l_1, \ldots, l_k$ and $n_i$ points on the line $l_i, i = 1, 2, \ldots, k$, find the maximum possible number of triangles with vertices at these points.
Izvor: Međunarodna matematička olimpijada, shortlist 1968