The probability the economy will boom is 10 percent, while the probability of a recession is 20 percent. Stock A is expected to return 15 percent in a boom, 9 percent in a normal economy, and lose 14 percent in a recession. Stock B should return 10 percent in a boom, 6 percent in a normal economy, and 2 percent in a recession. Stock C is expected to return 5 percent in a boom, 7 percent in a normal economy, and 8 percent in a recession. What is the standard deviation of a portfolio invested 20 percent in Stock A, 30 percent in Stock B, and 50 percent in Stock C?