Two things are mutually exclusive when they can't both happen at the same time In fact, if one of the events happens, then it prevents the others from happening For instance, a traffic signal can be green, red, or yellow, but cannot be two or more of those colors at the same time [Note: "Mutually exclusive" is not at all the same thing as "independent " Independence has to do with the probabilities not being affected by the outcome of the other event ]
If several events are mutually exclusive, then at most one can be "on" at any one time If there are 20 buttons, and they are mutually exclusive, with regard to being "on", then if one of them is "on", then the others must be "off"
The selection of one choice precludes the selection of any competitive choice Several machines can do an identical job in capital budgeting, but only one machine is selected and used