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PrintFirst 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