I came across the problem below:
Calvin has to cross several signals when he walks from his home to school. Each of these signals operate independently. They alternate every 80 seconds between green light and red light.At each signal, there is a counter display that tells him how long it will be before the current signal light changes. Calvin has a magic wand which lets him turn a signal from red to green instantaneously. However, this wand comes with limited battery life, so he can use it only for a specified number of times.
a. If the total number of signals is 2 and Calvin can use his magic wand only once, then what is the expected waiting time at the signals when Calvin optimally walks from his home to school?
b. What if the number of signals is 3 and Calvin can use his magic wand only once?
I found that it was asked before here but I am not able to understand the accepted answer. The accepted answer states that it takes 40 seconds for the lights to change from Red to Green and from Green to Red.
But should it not be 80 seconds as stated in the question?