Probability you will get a traffic light Red or Green

Question

So let's say regardless of the time of day, or day of the week you pass thru a prticular intersection 750 times in a given year. If you record the number of times you got the light either red or green can you then calculate the probability you will get the light Red in the future as you approach the light?

Answer 1

The easiest way is to time the light. If the time the light is green is 30 seconds and the time the light is red is 45 seconds (making the total time of a cycle 30 + 45 = 75 seconds), then the probability you will hit green is 30/75 or 40% and the probability you will hit red is 45/75 = 60%.

This, of course, assumes the light red/green frequency is constant AND that you randomly appear at the light. Please note that appearing at the light randomly might not be that easy if this light is amid a series of other lights. Lights are often timed in groups.