UKMT Grey Kangaroo, 2015

Combinatorics Difficulty 2.0 Junior Find the answer United Kingdom

Luis wants to make a pattern by colouring the sides of the triangles shown in the diagram. He wants each triangle to have one red side, one green side and one blue side. Luis has already coloured some of the sides as shown. What colour can he use for the side marked $x$ ?

(A) only green (B) only blue (C) only red (D) either blue or red (E) The task is impossible

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