4 The route used by a certain motorist in commuting to work contains two intersections with traffic signals. The probability that he must stop at the first signal is 0.5 and the probability that he...

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Extracted text: 4 The route used by a certain motorist in commuting to work contains two intersections with traffic signals. The probability that he must stop at the first signal is 0.5 and the probability that he must stop at the second signal is 0.4, and the probability that he must stop at least one of the two signals is 0.6. Let Si be the event that he must stop at first signal and S2 be the event that he must stop at the second signal. What is the probability that he must stop a. at both the signals? b. at exactly one signal? c. at the second signal given that he has not stopped at the first signal?