Minimum number of colours used for hats and ribbons
Source: Pan African Olympiad 2009
October 1, 2011
combinatorics proposedcombinatorics
Problem Statement
Consider children in a playground, where . Every child has a coloured hat, and every pair of children is joined by a coloured ribbon. For every child, the colour of each ribbon held is different, and also different from the colour of that child’s hat. What is the minimum number of colours that needs to be used?