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【OG20-P157-77题】
Al and Ben are drivers for SD Trucking Company. One snowy day, Ben left SD at 8:00 a.m. heading east and Al left SD at 11:00 a.m. heading west. At a particular time later that day, the dispatcher retrieved data from SD’s vehicle tracking system. The data showed that, up to that time, Al had averaged 40 miles per hour and Ben had averaged 20 miles per hour. It also showed that Al and Ben had driven a combined total of 240 miles. At what time did the dispatcher retrieve data from the vehicle tracking system?
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【答案】B
【解析】假设,AI出发x小时以后
20×3+20x+40x=240,
X=3,所以11.00之后三个小时,是在下午2.00时。
【知识点补充】
平均速度=总路程÷总时间
相遇路程=速度和×相遇时间
追及路程=速度差×相遇时间
题目讨论 (4条评论)

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+7想要730呀
设Ben用了t小时,Al t-3小时 ben走了20t. AL走了40t-120 20t+40t-120=240 t=6 8点+6小时=14点
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0 回复 2020-02-27 15:39:36
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Bella804
设B的时间为T, A的时间为T+3. 240=40*(T+3)+20T
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0 回复 2019-12-25 06:29:55
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J15
双方一起走过的路程是180,假设一起走了X小时,那么40x + 20x = 180,而不是直接除以2,因为他们俩的速度不一样
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0 回复 2019-06-13 14:40:51
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Kiana
设:B所用时间为t,则A所用时间为t+3 40(t-3)+20*t=240 ==>t=6 从8点过了6小时是下午2点
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0 回复 2018-07-02 14:09:55
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Deborah回复Kiana
B所用时间为T A所用时间为T-3不是T+3吧
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0 回复 2018-07-10 19:15:11
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