392 Part 4 Risk and Return 10. The following spreadsheet contains monthly returns for Cola Co. and Gas Co. for 2013. Using these data, estimate the average monthly return and volatility for each stock (see MyFinanceLab for the data in Excel format). Gas Co. Cola Co. Date 10.84% Jan 6.00% 1.28% Feb 2.36% Mar 1.86% 6.60% Apr 2.01% 1.90% 7.40% May 18.36% 0.26% June 1.22% July 2.25% 8.36% Aug 6.89% 2.46% Sep 6.04% 2.00% 13.61% 0.00% Oct Nov 3.51% 4.68% 0.54% 2.22% Dec X 11. Using the spreadsheet from Problem 10 and the fact that Cola Co. and Gas Co. have a correlation of 0.6083, calculate the volatility (standard deviation) of a portfolio that is 55% invested in Cola Co. stock and 45% invested in Gas Co. stock. Calculate the volatility by a. Using Eq. 12.4. b. Calculating the monthly returns of the portfolio and computing its volatility directly. c. How do your results compare