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National and Regional Contests
Nigeria Contests
2024 Nigerian MO Round 3
Problem 4
Problem 4
Part of
2024 Nigerian MO Round 3
Problems
(1)
polygon combinatorics
Source: 2024 Nigerian MO Senior Round 3 P4
4/28/2024
In an island shaped like a regular polygon of
n
n
n
sides, there are airports at each vertex of the island. The island would like to add
k
k
k
new airports into the interior of the island, but it must follow the following rules:\\
1
1
1
. It must be in the interior of the island (none on borders).\\
2
2
2
. No two airports can be at the exact same location.\\
3
3
3
. Every triple of
1
1
1
new and
2
2
2
old airports must form an isoceles triangle.\\
4
4
4
. No three airports can be collinear.\\Find the maximum value of
k
k
k
for each
n
n
n
[hide=Harder Version]Replace
1
1
1
new and
2
2
2
old with
1
1
1
old and
2
2
2
new.
combinatorics