AMC 8 1999 Problem 10

AMC8 1999 年第 10 题

概率★★☆☆☆

A complete cycle of a traffic light takes 60 seconds. During each cycle the light is green for 25 seconds, yellow for 5 seconds, and red for 30 seconds. At a randomly chosen time, what is the probability that the light will NOT be green?

一个红绿灯的完整周期为 60 秒。每个周期中，绿灯亮 25 秒，黄灯亮 5 秒，红灯亮 30 秒。在随机一个时刻，灯不是绿色的概率是多少？

A. $\displaystyle \frac{1}{4}$
B. $\displaystyle \frac{1}{3}$
C. $\displaystyle \frac{5}{12}$
D. $\displaystyle \frac{1}{2}$
E. $\displaystyle \frac{7}{12}$

正确答案 · Correct Answer

解析 · Solution

Solution 1

\displaystyle \frac{\text{time not green}}{\text{total time}} = \frac{R + Y}{R + Y + G} = \frac{35}{60} = \textbf{(E)}\ \frac{7}{12}

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