Question 20 (Mandatory] (2 points) For the previous question, what is the best point estimate for the difference treatment population mean - control population mean? 3.5 Q47 O19 O 37 O 3.3 Question 21 [Mandatory) (5 points) A random sample of 400 patients at a clinic is polled after their visits. Of the patients, 300 say they were satisfied with their visit. Which of the following is a 90% confidence interval for the true proportion of patients that are satisfied at the clinic? 0.75 +/-0.036 0.75 +/-0.045 0.75 +/-0.066 0.75 +/-0.15 0.75 +/- 0.005 Question 22 (Mandatory) (5 points) A medical device manufacturer wishes to estimate the difference in reported time to first failure for a device that is sold in rural and urban areas. They take a random sample of 500 from each area, The means obtained are 1.1 years for rural areas and 3.8 years for urban areas. Find the 95% confidence interval for the true difference in the population means. The population standard deviation for both areas is O.d years! )0.3+/-0.0400 0.3 +/-0.0496 0.3+/- 0.0350 0.3 +/- 0.0452 03 +7-0.0373