A particular brand of diet margarine was analyzed to determine the level of polyunsaturated fatty acid (in percent- ages). A sample of six packages resulted in the following data: 16.8, 17.2, 17.4, 16.9, 16.5,  17.1.

(a) Check the assumption that the level of polyunsaturated fatty acid is normally distributed.

(b) Calculate a 99% confidence interval on the mean p. Provide a practical interpretation of this interval.

(c) Calculate a 99% lower confidence bound on the mean. Compare this bound with the lower bound of the two-sided confidence interval and discuss why they are different.