Question 9.20 (pg. 429)

(a) Construct a 90% confidence interval for the proportion of college freshmen who carry a credit card balance from month to month. Enter your answer as two decimals separated by a comma. [Example: .1, .2].

(b) Construct a 90% confidence interval for the proportion of college seniors who carry a credit card balance from month to month. Enter your answer as two decimals separated by a comma. [Example: .1, .2].

(c) Explain why the two 90% confidence intervals from parts (a) and (b) are not the same width. Select an answer Because the standard deviations are different Because the formula used is different Because the sample sizes are different