Here are returns and standard deviations for four investments, Return Standard Deviation ( Treasury bills Stock P Stock Stock R 3.5 11.5 13.5 23.5 35 28 Calculate the standard deviations of the following portfolios. a. 50% in Treasury bills. 50% in stock P (Enter your answer as o 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