Margin of Error Confidence Intervals

A survey of 800 women shoppers found that 17% of them shop on impulse.  What is the 98% confidence interval for the true proportion of women shoppers who shop on impulse? 

• 0.148 < p < 0.192

• 0.136 < p < 0.204

• 0.144 < p < 0.196

• 0.139 < p < 0.201

It was found that in a sample of 90 teenage boys, 70% of them have received speeding tickets.  What is the 90% confidence interval of the true proportion of teenage boys who have received speeding tickets? 

• (0.621, 0.780)

• (0.591, 0.812)

• (0.584, 0.830)

• (0.615, 0.805)

Which of the following values below represents the critical value for a 98% confidence interval?

• 2.326

• 2.054

• 1.645

• 3.091

If the margin of error in a confidence interval is 8 and the sample mean is 200, what is the lower bound of the confidence interval?

• 192

• 196

• 200

• 208

A 95% confidence interval for a population mean is calculated as (150, 210). What is the margin of error?

• 30

• 60

• 180

• 360

A 99% confidence interval for a population mean is (100, 200). What is the margin of error?

• 50

• 100

• 150

• 200

• 1.64

• 1.96

• 2.33

• 2.58

A survey estimates that 45% of voters favor candidate A with a margin of error of 4%. What is the confidence interval for the proportion of voters who favor candidate A?

• (0.41, 0.49)

• (0.39, 0.51)

• (0.43, 0.47)

• (0.45, 0.49)

To decrease the margin of error in a confidence interval, you should:

• Increase the confidence level

• Decrease the sample size

• Increase the sample size

• Decrease the confidence level

If you want to construct a confidence interval with a smaller margin of error without changing the sample size, what could you do?

• Increase the confidence level

• Decrease the confidence level

• Increase the variability in the sample

• Decrease the variability in the sample