有人能说说红绿灯的题咋做么？

1。 DS﹕路燈按綠 25秒﹐黃5秒﹐紅30秒變化。問正午剛過1秒鐘是否3燈都綠。(1) 第一個燈變紅後15秒第2燈變紅﹐(第一燈紅)30秒後第3燈變紅。 (2) 正午前35分鐘的時刻沒一個是綠的。

是A么？

路燈按綠 25秒﹐黃5秒﹐紅30秒變化

从这"按"字来看, 就算它G-Y-R-G-Y-R循环.

1)sufficient. 红和非红(绿+黄)正好30秒间隔. 那第一灯和第三灯正好差开, 所以任何时刻一灯和三灯不会同绿.

2) not sufficient. 35分钟前若是黄, 此刻为绿. 35分钟前若是红, 此刻有3种都有可能, 所以2 alone is not sufficient.

哈! 这题够拗的.

LZ 第一个解释容易理解. 第二个我就不怎么懂了.

(2) Not sufficient, but my understanding is kind of different:

-if, 35 minutes ago, right on the fifth second of 5-second duration, traffic light is yellow. That means: the very end of every minute for this light, its yellow, so the first second after noon, this light is RED?

If, 35 minutes ago, this light is not right on the fifth second, and its yellow. then the first second after noon, this light is still YELLOW.

-if, 35 minutes ago, right on the 30th second of 30-second duration, traffic light is red. That means: the very end of every minute for this light, its red, so the first second after noon, this light is GREEN?

By the same token, If, 35 minutes ago, this light is not right on 30th second of 30-second duration, the light is still RED.

Is my understanding correct?

Thanks!

you are absolutely correct.I misread 35 minutes to 35 seconds.

 正午前35分鐘的時刻沒一個是綠的???

这个35分钟是时间段还是35分钟前的那个时间点??

要是整个时间段的话(2)肯定是对的,选D

时间点的话就不一定了,选A

请NN回答