Quiz 11
Name: _____________________________
December 4, 2009
Studies have shown that 22% of all orders from Amazon.com are from firsttime customers.
A simple
random sample of 90 orders is taken to estimate the proportion of firsttime customers to see if this is
actually true.
a.
What are the sampling distribution and parameters of
p
?
~
=.
, =.
.
= .
p
Normalμ
22
σ
221 2290
0 044
b.
What is the probability the proportion of firsttime
customers in 2009 is more than 25%?
>.
=
>.
.
.
= 
.
= .
Pp
25
PZ
25 220 044
1 Φ0 68
0 248
c.
What is the probability the proportion of firsttime customers in 2009 is within 5% of the population
proportion, 22%?
.
< <.
=  .
.
<
< .
.
=
.

 .
= .
P 17 p
27
P 0 050 044 Z 0 050 044
Φ1 14 Φ 1 14
0 746
~
=
,
=
x
Normalμ
EX
σ2
VarXn
xi
~
=
,
=
Normalμ
nEX
σ2
nVar X
~
=
= ,
=

p
Normalμ
xn
p
σ2
p1 pn
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Quiz 11
Name: _____________________________
December 4, 2009
It has been reported that in the United States, 44% of senior citizens are now using the internet.
A sample
of 70 senior citizens was taken to estimate the proportion of internet users to see if this is a reasonable
estimate.
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 Fall '08
 MARTIN
 Simple random sample, firsttime customers, σ2=nVar X p~Normalμ=xn=p

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