2. 外语
  3. The traffic light changes color in the order of Green-Yellow-Red, and the time duration for each color is 45s, 5s, 40s respectiv

The traffic light changes color in the order of Green-Yellow-Red, and the time duration for each color is 45s, 5s, 40s respectiv

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问题 The traffic light changes color in the order of Green-Yellow-Red, and the time duration for each color is 45s, 5s, 40s respectively. How many seconds at most can the red light appear in a period of 5 minutes?
选项 A、150s
B、120s
C、180s
D、160s
E、100s
答案A
解析 一共5分钟即300秒，Green-Yellow-Red按照顺序亮一次需要45+5+40=90秒，要使红灯在这个300秒间隔内出现时间最长，那么这300秒间隔可以从红灯开始亮算起，这样经过40秒红灯后，余下260秒再开始Green-Yellow-Red循环，一个循环需要90秒，那么只能做两个循环，剩下260-90×2=80秒，按照Green-Yellow-Red顺序亮，绿灯亮去掉45秒。黄灯亮去掉5秒，还剩下80-45-5=30秒红灯亮。
那么在这300秒内，红灯最大一共亮40+40×2+30=150秒。
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