 
Summary: Math 140
Introductory Statistics
Professor Bernardo Ábrego
Lecture 11
Sections 5.1, 5.3
5.1 Models of Random Behavior
Outcome: Result or answer obtained from a
chance process.
Event: Collection of outcomes.
Probability: Number between 0 and 1 (0%
and 100%). It tells how likely it is for an
outcome or event to happen.
P = 0 The event cannot happen.
P = 1 The event is certain to happen.
5.1 Models of Random Behavior
If the probability that event A happens is
denoted P(A), then the probability that event
A doesn't happen is P(not A) = 1  P(A).
The event not A is called the complement of
event A.
