The amount of nitrogen oxides in the air at a busy intersection was measured on 30 randomly selected days. The mean concentration was measured as 41.5 ug m-3, and the standard deviation was estimated...

Extracted text: The amount of nitrogen oxides in the air at a busy intersection was measured on 30 randomly selected days. The mean concentration was measured as 41.5 ug m-3, and the standard deviation was estimated to be 11.2 µg m-3. a. Determine the 95% confidence interval for the mean nitrogen oxide concentration. b. How many samples would be necessary to estimate the mean nitrogen oxide concentration within + 5% with 95% confidence?