The trade volume of a stock is the number of shares traded on a given day. The following data, in millions (so that 6.16 represents 6,160,000 shares traded), represent the volume of PepsiCo stock traded for a random sample of 40 trading days in 2014.

(a) Use the data to compute a point estimate for the population mean number of shares traded per day in 2014.
(b) Construct a 95% confidence interval for the population mean number of shares traded per day in 2014. Interpret the confidence interval.
(c) A second random sample of 40 days in 2014 resulted in the data shown next. Construct another 95% confidence interval for the population mean number of shares traded per day in 2014. Interpret the confidence interval.

(d) Explain why the confidence intervals obtained in parts (b) and (c) are different?