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UKMT Junior Kangaroo, 2019

Algebra Difficulty 2.0 Junior Find the answer United Kingdom

Geraint always cycles to work, leaving at 8am every morning. When he averages 15 km/h, he arrives 10 minutes late. However, when he averages 30 km/h, he arrives 10 minutes early. What speed should he average to arrive on time?

(A) $20$ km/h (B) $21$ km/h (C) $22.5$ km/h (D) $24$ km/h (E) $25$ km/h

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