2009 AMC 8 第 14 题
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所有题目均经美国数学协会（MAA）官方合法授权使用。
14.
奥斯汀和坦普尔相距 英里，由 号州际公路相连。邦妮从奥斯汀开车到她女儿在坦普尔的家，平均速度为每小时 英里。她把车留给女儿后，沿同一路线坐公交车返回奥斯汀，返程平均速度为每小时 英里。整个往返行程的平均速度是多少英里每小时？
Austin and Temple are miles apart along Interstate Bonnie drove from Austin to her daughter’s house in Temple, averaging miles per hour. Leaving the car with her daughter, Bonnie rode a bus back to Austin along the same route and averaged miles per hour on the return trip. What was the average speed for the round trip, in miles per hour?
小提示：
平均速度等于总路程除以总时间
Average speed is total distance divided by total time.
大提示：
两段 英里的路程所用时间不同
The two -mile trips take different amounts of time.
解答：
从奥斯汀到坦普尔用时 小时。从坦普尔到奥斯汀用时 小时。因此往返总时间为 小时。
往返总路程为 英里。因此往返平均速度为 英里每小时。
所以正确答案是 B。
The trip from Austin to Temple took hours. The trip from Temple to Austin took hours. This means that the total time for the round trip was hours.
The total distance of the round trip was miles. Therefore, the average speed for the round trip was miles per hour.
Thus, B is the correct answer.
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