A probability can be interpreted as the proportion of
times that a certain event can be expected to occur.
If the probability of an event is more than 1, then it will
occur more than 100
%
of the time (impossible).
4

PROBABILITY RULE B
All possible outcomes together must have probability 1.
Because some outcome must occur on every trial, the
sum of the probabilities for all possible outcomes must
be exactly one.
If the sum of all of the probabilities is less than one or
greater than one, then the resulting probability model
will be incoherent.
5

PROBABILITY RULE C
The probability that an event does not occur is 1 minus
the probability that the event does occur.
As a jury member, you assess the probability that the
defendant is guilty to be 0.80. Thus you must also
believe the probability the defendant is not guilty is
0
.
20 in order to be coherent (consistent with yourself).
If the probability that a flight will be on time is 0.70,
then the probability it will be late is 0.30.
6

PROBABILITY RULE D
If two events have no outcomes in common, they are
said to be
mutually exclusive
. The probability that one
or the other of two mutually exclusive events occurs is
the sum of their individual probabilities.
7

PROBABILITY RULE D
If two events have no outcomes in common, they are
said to be
mutually exclusive
. The probability that one
or the other of two mutually exclusive events occurs is
the sum of their individual probabilities.
Age of woman at first child birth
7

PROBABILITY RULE D
If two events have no outcomes in common, they are
said to be
mutually exclusive
. The probability that one
or the other of two mutually exclusive events occurs is
the sum of their individual probabilities.
Age of woman at first child birth
•
under 20: 25
%
7

PROBABILITY RULE D
If two events have no outcomes in common, they are
said to be
mutually exclusive
. The probability that one
or the other of two mutually exclusive events occurs is
the sum of their individual probabilities.
Age of woman at first child birth
•
under 20: 25
%
•
20-24: 33
%
7

PROBABILITY RULE D
If two events have no outcomes in common, they are
said to be
mutually exclusive
. The probability that one
or the other of two mutually exclusive events occurs is
the sum of their individual probabilities.
Age of woman at first child birth
•
under 20: 25
%
•
20-24: 33
%
•
25+:
?
7

PROBABILITY RULE D
If two events have no outcomes in common, they are
said to be
mutually exclusive
. The probability that one
or the other of two mutually exclusive events occurs is
the sum of their individual probabilities.
Age of woman at first child birth
•
under 20: 25
%
•
20-24: 33
%
•
25+:
?
•
Probability a woman is less than 25 when she has her
first child?

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- Spring '12
- zhao
- Probability, Standard Deviation, Probability theory