The common stock of Air United, Inc., had annual returns of 15.6 percent, 9.8 percent, 8.3 percent, and 13.3 percent over the last four years, respectively.

1.What is the arithmetic average of these returns?

2.What is the standard deviation of these returns?

3. Based on your calculation, what will be the range of its rate of return during 99% of the time? ( Hint: 99% confidence interval)