The correlation between Twitter, Inc.'s (Ticker: TWTR) returns and Diamondback Energy, Inc.'s (Ticker: FANG) returns is 0.327296456. Twitter, Inc. has a standard deviation of returns of 15.001814 percent while Diamondback Energy, Inc. has a standard deviation of returns of 16.795256 percent. Twitter, Inc. has an average return of 3.760061 percent while Diamondback Energy, Inc. has an average return of 1.190338 percent. Calculate the standard deviation of returns for a portfolio consisting of 48 percent Twitter, Inc. stock and 52 percent Diamondback Energy, Inc. stock.