A random sample of 1500 residential telephones in Phoenix found that 394 of the numbers were unlisted. A random sample in the same year of 1200 telephones in Scottsdale found that 313 were unlisted. A. Find a 95% confidence interval on the difference in the two proportions and use this confidence interval to determine 2010 whether there is a statistically significant difference in proportions of unlisted numbers between the two cities.
B. Find a 90% confidence interval on the difference in the two proportions and use this confidence interval to determine 2010 whether there is a statistically significant difference in proportions of unlisted numbers for the two cities.