行程问题：

 

A bee sat on the head of a horse rider whose horse was trotting eastbound at a steady five miles per hour. Some distance ahead on the same path, another horse and rider were approaching westbound, also at five miles per hour. When the two horses were 20 miles apart, the bee left the first horse rider and flew toward the second horse at a rate of ten miles per hours. Upon reaching the second horse, the bee immediately turned around and flew back at the same rate to the first horse. If the bee kept up this performance until the two riders met, how far (in miles) did he travel from the moment he left the first horse rider?

 

A) 10    B) 20    C) 30   D) None of the above

参考答案：B

解析：两匹马距离是20里，相向而行，两匹马的速度都是5里每小时，因此，相遇的时间是2小时后，蜜蜂在这段时间内，以不变的速度10里每小时的速度往返，已知蜜蜂飞行的时间和速度，可以求出蜜蜂这段时间飞行距离是20里。

 

One day, a motorist came to a hill that was ten-mile drive up one side and a ten-mile drive down the other. He drove up the hill at an average of 30 miles per hour. How fast will he have to drive down the other side to average 60 miles per hour for the entire 20-mile distance? (miles per hour)

 

A) 30    B) 60    C) 90   D) None of the above

参考答案：D

解析：上坡速度是30里每小时，上坡的距离与下坡的距离相同，都是10里，如果上下坡平均速度是60里每小时，求下坡的速度应该是多少？已知总路程、平均速度、上下坡距离个上坡速度，可以设下坡速度为x列方程。即20除以60等于10除以30加上10除以x，计算x无解， 因此，选D。

 

Each day, Sal swims a lap 1 second faster than on the day before. If Sal swims a lap in 60 minutes on the 1st day, on what day does he swim a lap in 10% less time than the 1st day?

A) 359th    B) 360th    C) 361st   D) 362nd

 

参考答案：C

解析：第二天总比第一天游泳时间快一秒，如果第一天游泳用时60分钟，那么哪一天游泳时间比第一天少百分之十，百分之十的时间为6分钟，即360秒，本题关键是别忘了第一天，第二天少了一秒，第三天比第一天少了两秒，因此，少360秒，应该在第361天。

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