Events in a probability experiment can be classified as Simple and Compound events. When an event cannot be broken into smaller events it is known as a Simple event. Simple events have only one outcome. This against the outcomes for a compound event is not restricted to a single outcome. Compound events are also known as multiple events as they can be viewed as the simultaneous occurrence of more than one event. In real world experiences, we require to deal with Compound events more often than with Simple Events. For this purpose specific rules/formulas are derived for computing the probability of compound events.
Let us see, how compound events are defined and how their probabilities are computed.

An event that consists of two or more simple events is called a compound event.For example, when a die is thrown, the event of number 1 turning up is a simple event.
The event of getting an odd number consists of three simple events of getting 1, getting 3 and getting 5.
Compound events can be defined either as union or as intersection of two events.
Formulas to compute the probability of compound events are derived based on the whether the events
are mutually exclusive, mutually inclusive or independent.

Addition Rules for probability

Rule 1:
When two events A and B are mutually exclusive, the probability that A or B will occur is
P(A or B) = P(A) + P(B)

Rule 2:
If A and B are not mutually exclusive (meaning they are mutually inclusive) then
P(A or B) = P(A) + P(B) - P(A and B).

Multiplication Rule for probability

When A and B are independent events, the probability of both happening is
P(A and B) = P(A) . P(B).