Skip to main content
OlympiadHQ

Browse · MathNet

Print

First Round, January 2019

Netherlands 2019 counting and probability

Problem

In a table with two rows and five columns, each of the squares is coloured black or white according to the following rules: Two adjacent columns may never have the same number of black squares. Two -squares that overlap in one column may never have the same number of black squares. How many possible colourings of the table comply with these rules?
Solution
D) 20
Final answer
D) 20

Techniques

Coloring schemes, extremal argumentsRecursion, bijection