Can you explain?I am getting different numbers from provided answer

5. Assume that an investment is forecasted to produce the following returns: a 20% probability of a 12% return; a 50% probability of a 16% return; and a 30% probability of a 19% return What is the standard deviation of return for this investment? A) 5.89% B) 16.1% C) 2.43% D) 15.7% Answer: C