Problem:
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?
Answer Choices:
A. 41​
B. 31​
C. 125​
D. 21​
E. 127​
Solution:
total time time not green ​=R+Y+GR+Y​=6035​=127​.
OR
The probability of green is 6025​=125​. so the probability of not green is 1−125​=127​.
Answer: E​.
The problems on this page are the property of the MAA's American Mathematics Competitions