You find a certain stock that had returns of 22 percent, -21 percent, and 32 percent for three of the last four years. Suppose the average return of the stock over this 4-year period was 10 percent.

a) What was the stock's return for the missing year?

b) Calculate the variance and the standard deviation of the stock's return?

c) Which one, variance or standard deviation, is more commonly used as a measurement of risk in investment? Explain your answer.