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Colored points on a circle

Source: SAMO Senior Round 3 2012 Problem 3

September 6, 2012
combinatorics unsolvedcombinatorics

Problem Statement

Sixty points, of which thirty are coloured red, twenty are coloured blue and ten are coloured green, are marked on a circle. These points divide the circle into sixty arcs. Each of these arcs is assigned a number according to the colours of its endpoints: an arc between a red and a green point is assigned a number 11, an arc between a red and a blue point is assigned a number 22, and an arc between a blue and a green point is assigned a number 33. The arcs between two points of the same colour are assigned a number 00. What is the greatest possible sum of all the numbers assigned to the arcs?