According to a Field Poll conducted February 8 - 17, 2005, 79% of California adu

Question

According to a Field Poll conducted February 8 - 17, 2005, 79% of California adults (actual results are 400 out of 506 surveyed) feel that "education and our schools" is one of the top issues facing California. We wish to construct a 90% confidence interval for the true proportion of California adults who feel that education and the schools is one of the top issues facing California. Find a 90% confidence Interval for the population proportion. (Round your answers to three decimal places.) (____, ____) A random digit dialing telephone survey of 880 drivers asked, "Recalling the last ten traffic lights you drove through, how many of them were red when you entered the intersections?' Of the 880 respondents, 176 admitted that at cast one light had been red. Give a 95% confidence interval for the proportion of all drivers who ran one or more of the last 10 red lights they encountered. (Use the plus four method. Round your answers to four decimal places.) ____ to _____

Explanation / Answer

1) p=0.79 ; n=506

std error =(p(1-p)/n)1/2 =0.018

for 90% CI, z=1.645

hence confidence interval =sample mean -/+ z*Std error =0.7602 ; 0.8198

2)

p=176/880=0.2 ; n=880

std error =(p(1-p)/n)1/2 =0.0135

for 95% CI, z=1.96

hence confidence interval =sample mean -/+ z*Std error =0.1736 ; 0.2264

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