Problem 8-7 Portfolio risk and return Here are returns and standard deviations for four investments. Treasury bills Stock P Stock 2 Stock R Return (%) 5.0 8.0 16.0 21.0 Standard Deviation (%) 0 15 29 26 Calculate the standard deviations of the following portfolios. a. 50% in Treasury bills, 50% in stock P. (Enter your answer as a percent rounded to 2 decimal places.) Standard deviation % b. 50% each in Q and R, assuming the shares have: (Do not round intermediate calculations. Enter your answers as a percent rounded to 2 decimal places.) Standard Deviation % Perfect positive correlation Perfect negative correlation No correlation % %