2018 IMO problem 4 || This one is hard!

International Mathematical Olympiad (IMO) is an annual Mathematics competition for pre-college students. IMO was first held in 1959, and in 2019, over 100 countries participated in the event. Today, we are going over problem 4 from 2018 IMO.

The problem is as follows: 2 players taking turn placing stones on a 20x20 board under some rules. The game stops if a player can no longer place a stone. Find the number of stones that the first players can always place.

Video information:

[alkankondo]

Wow! Such an elegant and easy-to-understand solution to what is, at first, a very complex problem! Great explanation!!

[jeremy]

Neat solution! I really like the pacing and visuals... starting with an example game and then moving on to show the partitioning and such.

[VibingMath]

I like the partition way to simplify the problem, and it's somehow related to rotational symmetry? Nice video! This question is real hard to think in short time in a competition

[ghauramahabaduge]

Nice problem for a P4 by the way but P5 of 2017 was nicer

[ghauramahabaduge]

This is not that hard I did it in the Olympiad in 2018

A memorable moment

[ericarodrigues]

Could you put subtitles in Portuguese? (I'm from Brazil and I understand little English), thanks