Red blood cell counts are normally distributed with a standard deviation of 0.68 cells per micro liter. A simple random sample of 50 adults is obtained, and each person's red blood cell count (in cells per microliter) is measured. The sample mean is 5.33 cells per micro liter. Find a 95% confidence interval for the true mean red blood cell count. 5.33 0.188 500.188 O 5.33 0.096 O 5.33 0.68