Question

一个交通灯的完整周期为 $60$ 秒。每个周期中绿灯 $25$ 秒，黄灯 $5$ 秒，红灯 $30$ 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 $60$ 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?

$\dfrac{1}{4}$

$\dfrac{1}{3}$

$\dfrac{5}{12}$

$\dfrac{1}{2}$

$\dfrac{7}{12}$

答案：E

知识点：几何概率对立事件概率

难度评级：980

解答：

在一个周期中，交通灯不是绿灯的时间为 $30 + 5 = 35$ 秒。

所以不是绿灯的概率为 $\dfrac{35}{60} = \dfrac{7}{12}.$

所以正确答案是 E。

During a given cycle, the light is not green for $30 + 5 = 35$ seconds.

Then the probability that it is not green is $\dfrac{35}{60} = \dfrac{7}{12}.$

Thus, E is the correct answer.

1999 AMC 8 第 10 题

答案：E

难度评级：980

解答：

其他年份的第 10 题