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UKMT Grey Kangaroo, 2023

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

Some mice live in three neighbouring houses. Last night, every mouse left its house and moved to one of the other two houses, always taking the shortest route. The numbers in the diagram show the number of mice per house, yesterday and today. How many mice used the path at the bottom of the diagram?

(A) $9$ (B) $11$ (C) $12$ (D) $16$ (E) $19$

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