Hint 1

There are two traffic lights on Fred’s route from home to work. Over the years Fred has tracked when he has to stop at these lights. He determined that 45% of the time he has to stop at the first light; 30% of the time he has to stop at the second light, and 20% of the time he has to stop at both lights.

Let A be the event that Fred has to stop at the first light. Let B be the event that Fred has to stop at the second light. What is the probability that Fred has to stop at one or more lights on his way to work?