Examples
CH 4
1.
Calculate the mean for the discrete probability distribution
shown here.
X
2
4
5
10
P(X)
.2
.2
.3
.2
Answer:
µ
=
Σ
xp
(
x
) = 2(.2) + 4(.3) + 5(.3) + 10(.2) = 5.1
2.
Ladies Home Journal
polled its readers to determine the
proportion of wives who, if given a second chance, would
marry their husband. According to the responses from the
survey, 80% of wives would marry their husbands again.
Suppose a random and independent sample of
n
= 20 wives is
collected. Define the random variable X = the number of the
20 wives who would marry their husband again. Then we know
X is a binomial random variable. Find the probability that
more than 15 of the wives responded that they would marry
their husbands again.
Answer:
Let a success be a wife who would marry her husband
again.
Then
x
is a binomial random variable with
n
= 20 and
p
=
.
80.
(Use Table)
P
(
X
> 15) = 1 
P
(
X
≤
15) = 1  .370 = .630
3.
It has been stated that 20% of the general population donate
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 Fall '11
 leonidbekker
 Advertising, Probability, Probability theory, Discrete probability distribution, binomial random variable, gas tanks

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