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UKMT Junior Mathematical Challenge, 2016

Combinatorics Difficulty 3.0 AMC 10/12 Find the answer United Kingdom

Part of a wall is to be decorated with a row of four square tiles. Three different colours of tiles are available and there are at least two tiles of each colour available. Tiles of all three colours must be used. In how many ways can the row of four tiles be chosen?

(A) $12$ (B) $18$ (C) $24$ (D) $36$ (E) $48$

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