If the probability of observing a car (read: at least one car) in 20 minutes on a highway is 609/625, what is the probability of observing a car (read: at least one) in 5 minutes (assuming constant default probability)?

ans: 3/5 i.e. 60%

no car in 20 min: 16/625

no car in 5 min: (16/625)^1/4=2/5

car in 5 min 1-2/5= 3/5= 60%

ady