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UKMT Junior Kangaroo, 2022

Combinatorics Difficulty 2.0 Junior Find the answer United Kingdom

Andrew wants to write the numbers 1, 2, 3, 4, 5, 6 and 7 in the circles in the diagram so that the sum of the three numbers joined by each straight line is the same. Which number should he write in the top circle?

(A) $2$ (B) $3$ (C) $4$ (D) $5$ (E) $6$

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