The sodium content of twenty 300-gram boxes of organic cornflakes was determined. The data (in milligrams) are:
131.15, 130.69, 130.91, 129.54, 129.64,
128.77, 130.72, 128.33, 128.24, 129.65, 130.14, 129.29,
128.71, 129.00, 129.39, 130.42, 129.53, 130.12, 129.78,
130.92.
a) Test the claim that the mean sodium content of this brand of cornflakes differs from 130 milligrams at the significance level α = 0.05. Find the P value.
(b) Check that sodium content is normally distributed.
(c) Explain how the question in part (a) could be answered by constructing a two-sided confidence interval on the mean sodium content.