Question 484089
According to a February 2005 survey completed by the Pew Internet and American Life Project, about 36 million Americans, or 27% of Internet users, say they download either music or video files. Assuming the percentage is correct, use the normal approximation to the binomial to find the probability of the following in a survey of 2000 American Internet users.
a) At least 500 download music or video files
mean = np = 2000*0.27 = 540
std = sqrt(npq) = sqrt(540*0.73) = 19.85
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P(500 <= x <= 2000) = P(499.5 <= x <= 2000.5)
z(499.5) = (499.5-540)/19.85 = -2.0403
z(2000.5) = (2000.5-540)/19.85 = 3.7058
Approx = P(-2.0403 < z < 3.7058) = 0.5807
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Use the similar approximation procedure for the following:
b) At least 575 download music or video files
c) At most 520 download music or video files
d) At most 555 download music or video files 
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Cheers,
Stan H.