Democratic strategists are predicting (well, praying for) a good economy in 2024. They are looking at the following probabilities: 50% chance that there will be a boom, 40% chance that the economy will be flat or neutral and only a 10% chance of a recession. The expected returns on Ruppel Intl. shares are 15% in the event of a boom, 10% if the economy's flat and -20% in a recession. What's the standard deviation of these returns