You find a certain stock that had returns of 9%, -16%, 21% and 17% for four of the five years. (Assume the returns are normally distributed)

1. If the average return of the stock over this period is 10.3%, what was the stock's return for missing year?
2. What is the standard deviation of stock return?
3. What is the probability that next year return will be between 10.3% and 25.77%?
4. What is the probability that next year return will be between -5.17% and 25.77%