1999 AMC 8 第 10 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。
10.
一个交通灯的完整周期为 秒。每个周期中绿灯 秒，黄灯 秒，红灯 秒。在随机选取的一个时刻，交通灯不是绿灯的概率是多少？
A complete cycle of a traffic light takes seconds. During each cycle the light is green for seconds, yellow for seconds, and red for seconds. At a randomly chosen time, what is the probability that the light will NOT be green?
小提示：
不是绿灯就是红灯或黄灯
Not green means red or yellow
大提示：
用非绿灯时间除以总周期时间
Use time not green over total cycle time
解答：
在一个周期中，交通灯不是绿灯的时间为 秒。
所以不是绿灯的概率为
所以正确答案是 E。
During a given cycle, the light is not green for seconds.
Then the probability that it is not green is
Thus, E is the correct answer.
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