A survey of 850 U.S. adults found that 34% of people said that they would get no work done on Cyber Monday since they would spend all day shopping online. Find the 90% confidence interval of the true proportion. Round intermediate answers to at least five decimal places. Round your final answers to at least three decimal places.
Solution :
Given that,
Point estimate = sample proportion = = 0.34
1 - = 1 - 0.34 = 0.66
Z/2 = Z0.05 = 1.645
Margin of error = E = Z / 2 * (( * (1 - )) / n)
= 1.645 (((0.34 * 0.66 ) / 850)
= 0.027
A 90% confidence interval for population proportion p is ,
± E
= 0.34 ± 0.027
= ( 0.313, 0.367 )
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