Obtain the stock prices on Occidental Petroleum (OXY) for the period January 1, 2019 to December 31, 2019. What was the monthly standard deviation of COP stock during that period? What is the annual standard deviation? Do the same thing for the period January 1, 2020 to May 1, 2020. Do not use any EXCEL formulas such as=average or =stdev in your calculations. (Though you might want to use these formulas to check your results.) Please include excel table and graph, with at least 50 data points, along with brief detailed explanations of each step.