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CEMC Gauss (Grade 7), 2000

Number theory Difficulty 2.0 Junior Find the answer Canada

In the addition shown, a digit, either the same or different, can be placed in each of the two boxes. What is the sum of the two missing digits?
$\begin{array}{r} 863 \\ \square 91 \\ 7\square 8 \\ \hline 2182 \end{array}$

(A) $9$ (B) $11$ (C) $13$ (D) $3$ (E) $7$

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