There is a chance that she will hit Troy and then a chance that she will actually be late.
If Juanita bumps into Troy in the hallway between periods 2 and 3, there is a 25% chance that she will be late. If she does not bump into Troy, she will make it to class on time. If there is a 20% chance that Juanita will bunp into Troy. How likely it is that she will be late on any given day?