A new method is developed to determine the content of sodium in a biscuit sample. Student A gets the following results: 24.2, 23.9, 25.0, 23.7, and 25.2 mg, while student B obtains 22.6, 21.9, 23.2, and 23.1 mg.

(a) Report 95% confidence interval of their results individually. Why the standard deviations are non-zero?

(b) At the 95% confidence level, does one of them get more reproducible measurements?

(c) At the 95% confidence level, do they obtain different results? What about a 90% confidence level?

(d) According to the manufacturer, the sodium content in the biscuit is 24.0 mg. Comment whether student B’s results are reliable at a 90% confidence level.

(e) The results from student C are 25.3, 25.4, 24.9, 25.0, 23.2 and 24.5 mg. Determine whether there is an outlier at the confidence level of 95%? What about 90%?