A man jogs at 6 mph over a certain distance and walks hack over the same route at 4 mph. What is his average speed for the journ

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问题 A man jogs at 6 mph over a certain distance and walks hack over the same route at 4 mph. What is his average speed for the journey?

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答案4.8mph

解析 (mph英里/小时。设单程距离为x，平均速度=总距离/总时间=2x/(x/6+x/4)=4.8。)

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B类竞赛（英语专业本科专科）

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