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Baltic Way 2023 · Problem 9

Combinatorics

Determine if there exists a triangle that can be cut into 101 congruent triangles.

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Topics

Pigeonhole and extremal arguments

Solutions

Solution

Answer: Yes, there is. Choose an arbitrary positive integer mm and draw a height in the right triangle with ratio of legs 1:m1 : m. This height cuts the triangle in two similar triangles with similarity coefficient mm. The largest of them can further be cut into m2m^2 smaller equal triangles by splitting all sides in mm equal parts and connecting corresponding points with parallel lines. Thus a triangle can be split into m2+1m^2 + 1 equal triangles.

The figure shows this for m=4m = 4, but in our problem we must take m=10m = 10.

Diagram for the mathnet 01j0 1 of bw-2023-09.

Contest context

Results from Baltic Way 2023

10 teams

Mean score
0.5 / 5
Scores of 4 or 5
1 / 10
Estonia
0 / 5

Score distribution

09
10
20
30
40
51
All team scores
TeamScore
Germany0 / 5
Sweden5 / 5
Lithuania0 / 5
Poland0 / 5
Estonia0 / 5
Latvia0 / 5
Norway0 / 5
Denmark0 / 5
Finland0 / 5
Iceland0 / 5