If two trains are 120 miles apart and are traveling toward each other at a constant rate of 30 mph and 40 mph, respectively, how

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问题 If two trains are 120 miles apart and are traveling toward each other at a constant rate of 30 mph and 40 mph, respectively, how far apart will they be exactly 1 hour before they meet?

选项 A、10 miles
B、30 miles
C、40 miles
D、50 miles
E、70 miles

答案E

解析 若两辆火车相距120英里远,且分别以每小时30英里和每小时40英里的速度对开,问它们相遇前1小时时相距多远?
解:本题的正确答案是(E)。考生略加思考就知,本题根本就不需要计算。相遇前1小时,也就是两辆火车还要开1小时才能相遇,而两辆火车的速度分别是30英里/小时和40英里/小时,在1小时中两辆火车各行驶30英里和40英里,也就是相遇前1小时相距70英里。
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