Transcript 5.2

HOMEWORK QUESTIONS?
PROBABILITY MODELS
A probability model describes chance behavior by listing
the possible outcomes in the sample space and giving
the probability that each outcome occurs.
Example:
Color of Marble
Red
Green
Blue
Probability
0.4
0.1
0.5
BASIC RULES OF PROBABILITY
ARE THESE MUTUALLY EXCLUSIVE?
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Turning left and turning right
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Drawing a king and drawing an ace
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Tossing a coin
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Drawing a king and drawing an ace
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Turning your head and scratching your foot
ADDITION RULE FOR MUTUALLY EXCLUSIVE
If A and B are mutually exclusive, P(A or B) = P(A) + P(B)
For example, find the probability that you pull an ace or a
king out of a deck of cards.
ANOTHER EXAMPLE
In a game of soccer, the probability of scoring no goals
(event A) is 20%. The probability of scoring exactly 1
goal (event B) is 15%.
Find P(A and B)
Find P(A or B)
TWO-WAY TABLES
Students in a college statistics class wanted to find out how common it is for
young adults to have their ears pierced. They recorded data on two
variables – gender and whether the student had a pierced ear – for all 178
people in the class. Here is the two-way table describing their results.
Suppose we choose a student at random. Find the probability that the
student:
a) has pierced ears
b) is a male with pierced ears
c) is a male or has pierced ears
Define
events!
A – is male
B – has
pierced
ears
Gender
Yes
No
Total
Male
19
71
90
Female
84
4
88
Total
103
75
178
ONE MORE EXAMPLE
Let A be the event that the person is a female and B be
the event that the person is underweight. Try to
answer these on your own:
1. P(A) =
2. P(B) =
3. P(A or B) =
4. P(A and B) =
HOMEWORK
Pg 308 (39-50)
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