填空题 A man jogs at 6 mph over a certain distance and walks back over the same route at 4 mph. What is his average speed for the journey?
【正确答案】
【答案解析】8 mph[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。