A car travels the first half of a motorway journey at an average speed of 40 mph, and the second half of the journey at an avera

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问题 A car travels the first half of a motorway journey at an average speed of 40 mph, and the second half of the journey at an average speed of 60 mph. What is the average speed for the entire journey?

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答案48 mph.

解析 问题问的是汽车在高速公路上行驶的前半段平均速度为40 mph,后半段平均速度为60 mph。整个行程的平均速度是多少?假设全程为120英里,前半程(60英里/小时)需要60/40=15小时,后半程 (60英里/小时)需要60/40=1小时。所以全程120英里需要1.5+1=25小时,平均速度为。120/2.5=48 mph。
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