Fewer young people are driving. In 1983, 87% of 19-year-olds had a driver\'s lic
ID: 3045172 • Letter: F
Question
Fewer young people are driving. In 1983, 87% of 19-year-olds had a driver's license. Twenty-five years later that percentage had dropped to 75% (University of Michigan Transportation Research Institute website, April 7, 2012). Suppose these results are based on a random sample of 1200 19-year-olds in 1983 and again in 2008.
a. At 95% confidence, what is the margin of error and the interval estimate of the number of 19-year-old drivers in 1983?
Margin of error = (four decimal places) Interval estimate (to three decimal places) =
b. At 95% confidence, what is the margin of error and the interval estimate of the number of 19-year-old drivers in 2008? Round your answers to four decimal places.
Explanation / Answer
a.
std.dev=root(pq/n)=root(0.87*0.13/1200)=0.0095
margin of error*z
margin of error=1.96*0.0095=0.0186
interval=(0.83±0.019)=(0.811, 0.848)
b.
std.dev=root(0.75*0.25/1200)=0.0125
margin error=o.0125*1.96=0.0245
inteval=0.75±0.0245=(0.7255, 0.7745)
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