Placing checkers in circles
Source: Belarusian TST 2024
October 27, 2024
combinatorics
Problem Statement
Given positive integers and . Consider an equilateral triangular board with
side , which consists of circles: in the first (top) row there is one circle, in the second row there are
two circles, , in the bottom row there are circles (see the figure below). Let us place checkers on
this board so that any line parallel to a side of the triangle (there are such lines) contains no more
than checkers. Denote by the largest possible number of checkers in such a placement.
https://i.ibb.co/bJjjK1M/Image2.jpg
a) Prove that the following upper bound is true:
b) Find and
D. Zmiaikou