SOLUTION: Seven percent of the voters in Fiction County are members of the Libertarian Party. A polling organization compiles a supposedly random list of 1200 Fiction County voters. Eighty-o

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Question 1186282: Seven percent of the voters in Fiction County are members of the Libertarian Party. A polling organization compiles a supposedly random list of 1200 Fiction County voters. Eighty-one of the voters on the list turn out to be members of the Libertarian Party. What is the z-score for the number of Libertarians on this list?
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
81/1200=0.0675, p hat
z=(p hat-p(/sqrt(p*(1-p)/n)
=-0.0025/0.0072
=-0.35 (-0.3472)

Check with normal approximation
the sample proportion is 81/1200=0.0675
the sd is sqrt (np(1-p))=sqrt 81*0.9325= sqrt (75.53)=8.69
z=(x bar-mean)/sd
=(81-84)/8.69, where the 84 is 7% of the 1200 expected
=-3/8.69
=-0.35 (-0.3452)