Two outcomes are independent if the occurrence of one outcome has no effect on the occurrence of the other. For example, if a coin is tossed twice, the first outcome (H or T) has no effect on the second outcome (H or T).
There are two ways multiple events can take place in a single probability problem: either they can each occur separately (A or B) or they must occur together (A and B).
In some scenarios, the events do not have to occur together to have the desired result. One of the events is enough.
I will be happy today if I win the lottery OR have email.
“Or” means that either outcome is desired. With more possible desired outcomes, the probability is greater than for one event alone.
For independent events with “or,” add the probabilities of the events.
A fair six-sided die is rolled once. What is the probability of rolling a 5 or a 6?