Answer each of the following questions. To get full marks, you must show sufficient justification for your answer.

a) [2 marks] When the distribution of data values is highly skewed, which measure of variability/spread is better: the interquartile range or standard deviation? Briefly explain your answer.

b) [2 marks] When surveying shoppers at a supermarket, is it appropriate to use a simple random sampling method to select a sample? Briefly explain your answer.

c) [2 marks] Suppose that a 90% confidence interval for the population mean grade (in percentage) of all Stat 4800 students at Langara College is (65.6, 70.2). Explain why the following definition of this interval is wrong: "90% of all Langara students have grades that are between 65.6 and 70.2".