Problem 8-7 Portfolio risk and return Here are returns and standard deviations for four investments. Return Standard Deviation (%) 17 Treasury bills Stock P Stock Stock R 3.0 8.5 18.0 23.5 37 27 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.) Perfect positive correlation Perfect negative correlation No correlation Standard Deviation % % %