8. A stock had returns of 16.11 percent, 23.82 percent, 11.53 percent, and 9.58 percent over four of the past five years. The arithmetic average return over the five years was 13.16 percent. What was the stock return for the missing year?

9. A stock had returns of 17.59 percent, 7.11 percent, and 23.81 percent for the past three years. What is the standard deviation of the returns?