12.2 Conditional Probability 2011 January 26, 2011
Objectives:
•
Find conditional probabilities.
•
Use formulas and tree diagrams.
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12.2 Conditional Probability 2011
January 26, 2011
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12.2 Conditional Probability 2011 January 26, 2011
Conditional Probability:
Probability that contains a condition that  may limit the sample space for an event.
Looks like:   P ( B  |  A )
Sounds like:  "the probability of event  B , given event  A "
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12.2 Conditional Probability 2011 January 26, 2011
Finding Conditional Probabilities
Example #1:  The table shows the results of a class survey.
Find each conditional probability.
a.  P(went to the game | male) b.  P(female | went to the game)
Did you go to the  basketball game last night?
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12.2 Conditional Probability 2011 January 26, 2011 a.  Write the conditional probability problem.
b.  Find the answer.
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12.2 Conditional Probability 2011 January 26, 2011
Example #3:  Use the diagram to find the following conditional probability.
P (plastic | not recycled)
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12.2 Conditional Probability 2011 January 26, 2011
Lets find our own conditional probabilities...
Do you own a pet?
Example #4:
YES NO
Male a.
P (has a pet)
Female b.
P (female) c.
P (male and has a pet) d.
P (male | has a pet)
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12.2 Conditional Probability 2011 January 26, 2011
Example #5 :  Flighty Airlines Update
80% of its flights depart on time.
72% of its flights depart and arrive on time.
Find the probability that a flight arrives  on time, given that it departs on time.
FLIGHTY
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12.2 Conditional Probability 2011
Example #6:
January 26, 2011
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12.2 Conditional Probability 2011 January 26, 2011
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12.2 Conditional Probability 2011 January 26, 2011
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