This is a proof based problem added for learning purposes and does not accept submissions.
You can view the solution by clicking on the solution tab.
You can view the solution by clicking on the solution tab.
Given $8$ lines on a plane and no two of them are parallel. Prove that, at least two of them form an angle less than $23^\circ$.
Source: BdMO 2018 National Junior P6
We can move the lines such that they all intersect in one point. Notice that, this does not change the angle between any pair of lines. After moving, there are $16$ small angles summing to $360^\circ$. So, by Pigeonhole Principle, one of these angles must be less than or equal to $\frac{360^\circ}{16}=22.5^\circ$, which is less than $23^\circ$ and we are done.