Probability in Practice
(The trick is knowing when to apply which probability rule!)
Suggestions :
•
Read the Textbook.
I like it.
•
Do problems in book.
They have solutions.
•
Make a picture.
This helps to clarify sample spaces.
•
Do some more problems.
Example :
An Entertainment Weekly poll taken over
the weekend showed that people’s choice for Emmy
for best drama was (voters could pick only one
show)
•
Lost
44%
•
Six Feet Under
17%
•
24(?)
18%
•
The West Wing
11%
Suggestion
: Check to see if probabilities satisfy
requirements :
Let
A
be the event that a person likes a
particular show above.
1)
For any event
A
,
1
)
(
0
≤
≤
A
P
(all fine here)
2)
1
)
(
=
S
P
(umm . . .)
STAT 101106
Introduction to Statistics
117
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View Full DocumentProbabilities of events so far only add to 90%, so make a
new category called ‘Other’ and assign it a probability of
10%.
Question :
what is the probability that a person
picked at random would list
‘24’ or ‘The West Wing’
as best drama?
Help :
‘or’ means
P(A or B)
.
Use addition rule and
then think about whether events are disjoint.
P(24 or WestW) = P(24) + P(WestW)–P(24 and Westw)
Last probability is zero since can’t have two
favorite shows – i.e., these events are
disjoint :
P(24 and Westw)= 0.
So :
P(24 or WestW) = P(24) + P(WestW) = .18 + .11 = .29
Question :
what is the probability that three
randomly chosen people all pick “24” as their
favorite show?
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 Fall '05
 JonathanReuningSchererDonaldGreen
 Conditional Probability, Probability, Probability theory, Type I and type II errors, Initialisms

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