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CEMC Gauss (Grade 8), 2006

Number theory Difficulty 2.0 Junior Find the answer Canada

In the addition of two $2$ -digit numbers, each blank space, including those in the answer, is to be filled with one of the digits $0, 1, 2, 3, 4, 5, 6$ , each used exactly once. The units digit of the sum is

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

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