UKMT Grey Kangaroo, 2020

Combinatorics Difficulty 2.0 Junior Find the answer United Kingdom

Aisha has a strip of paper with the numbers 1, 2, 3, 4 and 5 written in five cells as shown. She folds the strip so that the cells overlap, forming 5 layers. Which of the following configurations, from top layer to bottom layer, is it not possible to obtain?

(A) $3, 5, 4, 2, 1$ (B) $3, 4, 5, 1, 2$ (C) $3, 2, 1, 4, 5$ (D) $3, 1, 2, 4, 5$ (E) $3, 4, 2, 1, 5$

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