SOLUTION: Among U.S. households, 24% have telephone answering machines. If a telemarketing campaign involves 2,500 households, find the probability that more than 650 have answering machines

Question 62115This question is from textbook Elementary Statistics
: Among U.S. households, 24% have telephone answering machines. If a telemarketing campaign involves 2,500 households, find the probability that more than 650 have answering machines This question is from textbook Elementary Statistics

Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Among U.S. households, 24% have telephone answering machines. If a telemarketing campaign involves 2,500 households, find the probability that more than 650 have answering machines.
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The std deviation of the sample proportions is sqrt{pq/n)
=sqrt(0.24*0.76/2500)=0.008
The sample proportion is 650/2500=0.26
Convert 0.26 to a z-score,as follows:
z(0.26)=[0.26-0.24]/0.008=2.34
So, P(X>650)=P(z>2.34)=0.009 or 0.9%
Cheers,
Stan H.

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