2014 AMC 8 第 25 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。
25.
一段笔直的一英里高速公路关闭，路宽 英尺。Robert 沿图示由半圆组成的路径骑自行车。如果他以每小时 英里的速度骑行，走完这一英里路段需要多少小时？
注意： 英里等于 英尺
A straight one-mile stretch of highway, feet wide, is closed. Robert rides his bike on a path composed of semicircles as shown. If he rides at miles per hour, how many hours will it take to cover the one-mile stretch?
Note: mile = feet
小提示：
每个半圆让 Robert 沿公路前进 英尺
Each semicircle advances Robert feet along the highway.
大提示：
比较半圆弧长与其直径
Compare the length of a semicircle to its diameter.
解答：
每个半圆让 Robert 沿公路前进 英尺，所以一英里路段需要 个半圆。
每个半圆直径为 英尺，因此弧长为 英尺。Robert 骑行总距离为 英尺，也就是 英里。
速度为每小时 英里，所以时间为 小时。
所以正确答案是 B。
Each semicircle advances Robert feet along the highway, so a one-mile stretch requires semicircles.
Each semicircle has diameter feet, so its arc length is feet. The total distance Robert rides is feet, which is miles.
At miles per hour, the time is hours.
Thus, B is the correct answer.
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