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UKMT Grey Kangaroo, 2025

Combinatorics Difficulty 2.0 Junior Find the answer United Kingdom

Adira keeps gold, red, black, pink and white pearls in five small boxes. Each box contains pearls of only one colour. The boxes are labelled as shown, and all the statements are true. Adira's friend Lilly wants to know which box contains the gold pearls. She may open exactly one of the five boxes to look inside. Which box must Lilly open to be certain which of the boxes contains the gold pearls?

(A) gold or red (B) pink or black (C) black or gold (D) not black (E) pink or white

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