2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/230999Let $B$ and $R$ be point sets (of {\em blue} and {\em red} points, respectively) in the plane, such that $P:=B\cup R$ is in general position, and $|P|$ is even. A line $\ell$ is {\em balanced} if it spans one blue and one red point, and on each open halfplane of $\ell$, the number of blue points minus the number of red points is the same. We prove that $P$ has at least $\min \{|B|,|R|\} $ balanced lines. This refines a result by Pach and Pinchasi, who proved this for the case $|B|=|R|$.Combinatorics52A37; 52C30text