Confidence Intervals for Proportions

A recent study of 750 Internet users in Europe found that 35% of Internet users were women.  What is the 95% confidence interval of the true proportion of women in Europe who use the Internet? 

• (0.321, 0.379)
• (0.317, 0.385)
• (0.309, 0.319)
• (0.305, 0.395)

A survey of 800 women shoppers found that 136 of them shop on impulse.  What is the 98% confidence interval for the true proportion of women shoppers who shop on impulse? 

• (0.148, 0.192)
• (0.136, 0.204)
• (0.144, 0.196)
• (0.139, 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)

A recent poll of 700 people who work indoors found that 278 of them smoke.  The researchers want to be 90% confident that this proportion is within 3.5%. Of the following, which is the smallest sample size that will satisfy the manufacturer's requirements?

• 550
• 450
• 600
• 220

The Academy of Orthopedic Surgeons states that 80% of women wear shoes that are too small for their feet. A researcher wants to be 95% confident that this proportion is within 3% of the true proportion.  Of the following, which is the smallest sample size that will satisfy the manufacturer's requirements?

• 690
• 540
• 320
• 780

A random sample 90% confident interval for the proportion of  20 five-year-old children that believe in Santa Clause is (0.790, 1.01). Would it be believable if you were told that only 50% of five-year old children believe in Santa Clause?     

• Yes
• No

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

• 2.326
• 2.054
• 1.645
• 3.091

Which of the following is the critical value for an 80% confidence interval?

• 1.282
• 1.036
• 1.960
• 0.841

Which of the following is the critical value for an 85% confidence interval?

• 1.44
• 1.54
• 1.04
• 1.65