When Jenny returns home from her local supermarket, she has to pass through three sets of traffic lights. During the last 50 times she did that, she had to stop her car at the first set of traffic lights on 30 occasions, while 10 times the first traffic light was green but she had to stop at the second one. Furthermore, 6 times when both the first and the second lights were green, she had to stop at the third. Next time she returns from the supermarket, what is the probability that she has to stop in at least one of the three sets of traffic lights?