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•
10.7 Roleplaying games.
The intelligence of a character in a game is determined by
rolling the foursided die twice and adding 1 to the sum of the spots. Start with your work
in the previous exercise to give a
probability model
(
sample space
and
probabilities
of
outcomes) for the character’s intelligence. Follow the method of Example 10.5.
•
Count how many ways each intelligence level can occur; the
probabilities
are counts/16.
•
10.9 Overweight?
Although the rules of
probability
are just basic facts about percents or
proportions, we need to be able to use the language of
events
and their
probabilities
.
Choose an American adult at random. Define two
events
:
•
A
= the person chosen is obese
•
B
= the person chosen is overweight, but not obese
•
According to the National Center for Health
Statistics
,
P
(
A
) = 0.32 and
P
(
B
) = 0.34.
•
(a) Explain why
events
A
and
B
are
disjoint
.
•
(b) Say in plain language what the
event
“
A
or
B
” is. What is
P
(
A
or
B
)?
•
(c) If
C
is the
event
that the person chosen has normal weight or less, what is
P
(
C
)?
•
(a)
Event
B
specifically rules out obese
subjects
.
(b)
“The person chosen is overweight
or obese.”
P
(
A
or
B
) = 0.66.
(c)
0.34.
•
10.13 Working out.
Choose a person aged 19 to 25 years at random and ask, “In the past
seven days, how many times did you go to an exercise or fitness center or work out?”
Call the response
X
for short. Based on a large
sample survey
, here is a
probability model
for the answer you will get:
4
•
•
(a) Verify that this is a legitimate discrete
probability model
.
•
(b) Describe the
event
X
< 7 in words. What is
P
(
X
< 7)?
•
(c) Express the
event
“worked out at least once” in terms of
X
. What is the
probability
of
this event?
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(a)
The eight
probabilities
have sum 1.
(b)
“The
subject
worked out fewer than 7 days in
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 Fall '11
 
 Probability

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