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UKMT Intermediate Mathematical Challenge, 2023

Number theory Difficulty 2.0 Junior Find the answer United Kingdom

Across: 1. A power of 5, 2. A power of 4. Down: 1. A power of 6. Eight of the digits from 0 to 9 inclusive are used to fill the cells of the crossnumber. What is the sum of the two digits which are not used?

(A) $12$ (B) $13$ (C) $14$ (D) $15$ (E) $16$

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