Suppose that a safety group surveyed 1,200 drivers. Among those surveyed, 66% sa

Question

Suppose that a safety group surveyed 1,200 drivers. Among those surveyed, 66% said that careless or aggressive driving was the biggest threat on the road, and 37% said that cell phone usage by other drivers was the driving behavior that annoyed them the most. Based on these data and assuming that the sample was a simple random sample, construct and interpret a 90% confidence interval estimate for the true proportion in the population of all drivers who are annoyed by cell phone users. The confidence interval estimate is D (Round to three decimal places as needed. Use ascending order.)

Explanation / Answer

p is 0.37 and N is 1200

z for 90% confidence is 1.65

thus lower limit is p-z*sqrt(p*(1-p)/N)=0.37-1.65*sqrt(0.37*(1-0.37)/1200)=0.347

upper limit is p+z*sqrt(p*(1-p)/N)=0.37+1.65*sqrt(0.37*(1-0.37)/1200)=0.393

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