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