An economist reports that 315 out of a sample of 900 middle-income american households actively participate in the stock market. [you may find it useful to reference the z table.] a. construct the 99% confidence interval for the proportion of middle-income americans who actively participate in the stock market. (round intermediate calculations to at least 4 decimal places. round "z" value and final answers to 3 decimal places.) b. can we conclude that the percentage of middle-income americans who actively participate in the stock market is not 45%? yes, since the confidence interval contains the value 0.45. yes, since the confidence interval does not contain the value 0.45. no, since the confidence interval contains the value 0.45. no, since the confidence interval does not contain the value 0.45.