## Generalization of APMO 2015, problem 4

Discussion on Asian Pacific Mathematical Olympiad (APMO)
Masum
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Joined: Tue Dec 07, 2010 1:12 pm

### Generalization of APMO 2015, problem 4

Can this problem from APMO 2015 be generalized for any $k\leq2n$? Which means:
Prove or disprove: In a plane, there are $2n$ distinct lines where $n$ is a positive integer. Among them, $n$ lines are colored blue and $n$ lines are colored red and no two lines are parallel. Let $\mathcal{B}$($\mathcal{R}$) be the set of all points that lie on at least one blue(red) line. Prove that, there exists a circle that intersects $\mathcal{B}$ and $\mathcal{R}$ in exactly $k$ points where $k\leq2n$.
One one thing is neutral in the universe, that is $0$.