Company A's manager believes that economic conditions during the next year will be strong, normal, or weak, and they think that the firm's returns will have the probability distribution shown below. What's the standard deviation of the estimated returns? (Hint: Use the formula for the standard deviation of a population, not a sample. Do not round intermediate calculations.) Economic Conditions Prob. Return Strong 25% 28.0% Normal 35% 15.0% Weak 40% 13.0%