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UKMT Junior Mathematical Challenge, 2020

Combinatorics Difficulty 1.0 Junior Find the answer United Kingdom

This $3$ by $3$ grid shows nine $1\text{ cm} \times 1\text{ cm}$ squares and uses $24\text{ cm}$ of wire. What length of wire is required for a similar $20$ by $20$ grid?

(A) $400\text{ cm}$ (B) $420\text{ cm}$ (C) $441\text{ cm}$ (D) $800\text{ cm}$ (E) $840\text{ cm}$

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