Graph the $201518$ monthly returns of Pfizer Inc. $($PFE$)$ and Centene Corporation $($CNC$).$ Visually compare the month$-$to$-$month variation in monthly returns of both stocks. Which stock appears to have greater variation?

b$.$ Calculate the average monthly return, standard deviation, and minimum and maximum monthly returns of the S&P $500$ and the ten stocks.

c$.$ Compare the average monthly return and standard deviation of Pfizer Inc. and Centene Corporation. What do you notice about the risk return relationship? Compare the average monthly return and standard deviation of Pfizer Inc. and McKesson Corporation. What do you notice about the risk return relationship?