Question 438069
 in a survey , 65% of Americans said they own an answering machine. 
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If 20 Americans are selected randomly 
a) find the probabilities that at least 18 people own an answering machine
P(18<= x <=20) = 1-binomcdf(20,0.65,17) = 0.0121
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b) find the mean and the standard deviation the number of people owning an answering machine .
mean = np = 20*0.65 = 13
std = sqrt(13*0.35) = 2.1331
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cheers,
Stan H.
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