At 9:00 a. m. train T left the train station and two hours later train S left the same station on a parallel track. If train T a

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问题 At 9:00 a. m. train T left the train station and two hours later train S left the same station on a parallel track. If train T averaged 60 kilometers per hour and train S averaged 75 kilometers per hour until S passed T, at what time did S pass T?

选项 A、2:00 p.m.
B、5:00 p.m.
C、6:00 p.m.
D、7:00 p.m.
E、9:00 p.m.

答案D

解析 火车T于上午9:00离开车站,两小时后,火车S离开同一车站,且运行在平行的轨道上。若火车T的平均速度为60Km/h,火车S在超过火车T之前的平均速度为75Km/h,在几点钟S超过T?
解:本题的正确答案为(D)。设x小时后S追上T,此时两火车运行的距离相等,即:(x+2)×60=x×75 => x=8,S在T出发10小时后,即7:00 p.m追上T。
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