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Number theory Difficulty 2.0 Junior Find the answer United Kingdom

What is the largest integer $k$ whose square $k^2$ is a factor of $10!$ ? $[10! = 10 \times 9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1.]$

(A) $6$ (B) $256$ (C) $360$ (D) $720$ (E) $5040$

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