Confidence Intervals and Sample Size

Find the critical value, z* for 97%

Which confidence would result in a wider interval (assuming nothing else changed), 91% or 97%?

Which of the following changes to a study would result in a narrower confidence interval?

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? 

This is notation from a different book. Identify the confidence interval used in the figure below if each shaded area is equal to 0.05.

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? 

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? 

Which of the following actions would produce a confidence interval with a smaller width assuming all other contingencies remained constant?

A sample of 20 cupcakes found the interval for average calories to be (150, 350). Which is the correct interpretation of the 95% confidence interval?

Thirty randomly selected students took the calculus final. If the sample mean was 92 and the standard deviation was 9.4, construct a 99 percent confidence interval for the mean score of all students from which the sample was gathered.