south trucking, inc. stock is expected to return 8.4 percent in a boom, 8.9 percent in a normal economy, and 9.2 percent in a recession. the probabilities of a boom, normal economy, and a recession are 6 percent, 92 percent, and 2 percent, respectively. what is the standard deviation of the returns on this stock? (round to six decimal places for intermediate calculation) group of answer choices .38 percent .55 percent .42 percent .06 percent .13 percent