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Chapter 7: Probability
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Rule 4:
The sum of the probabilities of all the simple events in a sample
space must equal to 1. Another way of saying this is to say that the
probability of the sample space in any experiment is always 1.
For example, if we consider the sample space for
Example 7-7
, there are 8
simple events. By the classical approach, each simple event has an equal
chance of occurring. That is, each simple event has a 1/8 chance of
occurring. When we sum these probabilities we will have (1/8 + 1/8 + 1/8 +
1/8 + 1/8 + 1/8 + 1/8 + 1/8) = 8 ×1/8 = 1.
Notes:
The closer the probability of an event is to one, the more likely that
the event will occur.
The closer the probability of an event is to zero, the less likely that the
event will occur.
The next section will introduce some other rules of probability. However,
these will deal with compound events.
Section Review
7-9 Other Rules of Probability
Here we will consider some other rules that will enable us to find
probabilities between events.
Compound Events
Sometimes, we may have to combine events in order to define another event.
Such events are called
compound events
.
e-Self Review