As an assistant to Rachel, you are asked to collect the monthly prices of each stock from Yahoo Finance from 11/23/2010 to 11/2/2015 (market booming time period), and then finish the following tasks : (WMT and CITI - both shown below) show excel formula and/or explain your answers.

1. Calculate monthly returns for each stock

2. Calculate the variance and average return for each stock

3. Construct the covariance matrix of these stocks

4. Use Excel Solver function to build the efficient frontier (with and without short sale)

5. Determine the optimal risk portfolio

6. Draw a graph showing the efficient frontier and the CAL line (one graph for the case with short sale and one graph without short sale)

Please use the following data:

Citi C

Date	Open	Close
11/2/2015	53.450001	53.830002
10/1/2015	49.419998	53.169998
9/1/2015	52.400002	49.610001
8/3/2015	58.619999	53.48
7/1/2015	56.009998	58.459999
6/1/2015	54.68	55.240002
5/1/2015	53.639999	54.080002
4/1/2015	51.369999	53.32
3/2/2015	52.419998	51.52
2/2/2015	47.200001	52.419998
1/2/2015	54.360001	46.950001
12/1/2014	53.799999	54.110001
11/3/2014	53.419998	53.970001
10/1/2014	51.68	53.529999
9/2/2014	51.779999	51.82
8/1/2014	48.59	51.650002
7/1/2014	47.419998	48.91
6/2/2014	47.599998	47.099998
5/1/2014	47.810001	47.57
4/1/2014	47.720001	47.91
3/3/2014	47.799999	47.599998
2/3/2014	47.84	48.630001
1/2/2014	52.029999	47.43
12/2/2013	52.959999	52.110001
11/1/2013	48.869999	52.919998
10/1/2013	48.849998	48.779999
9/3/2013	49.369999	48.509998
8/1/2013	52.84	48.330002
7/1/2013	48.5	52.139999
6/3/2013	52.060001	47.970001
5/1/2013	46.48	51.990002
4/1/2013	44.32	46.66
3/1/2013	41.560001	44.240002
2/1/2013	42.48	41.970001
1/2/2013	40.91	42.16
12/3/2012	34.959999	39.560001
11/1/2012	37.57	34.57
10/1/2012	33	37.389999
9/4/2012	29.530001	32.720001
8/1/2012	27.299999	29.709999
7/2/2012	27.469999	27.129999
6/1/2012	25.860001	27.41
5/1/2012	32.919998	26.51
4/2/2012	36.400002	33.040001
3/1/2012	33.52	36.549999
2/1/2012	31.27	33.32
1/3/2012	27.129999	30.719999
12/1/2011	27.08	26.309999
11/1/2011	28.92	27.48
10/3/2011	25.16	31.59
9/1/2011	30.93	25.620001
8/1/2011	39.34	31.049999
7/1/2011	41.529999	38.34
6/1/2011	40.990002	41.639999
5/2/2011	4.6	41.150002
4/1/2011	4.46	4.59
3/1/2011	4.7	4.42
2/1/2011	4.86	4.68
1/3/2011	4.78	4.82
12/1/2010	4.28	4.73
11/23/2010	4.15	4.2

Walmart WMT

Date	Open	Close
11/2/2015	57.290001	57.610001
10/1/2015	64.760002	57.240002
9/1/2015	63.799999	64.839996
8/3/2015	71.839996	64.730003
7/1/2015	71.599998	71.980003
6/1/2015	74.690002	70.93
5/1/2015	78.199997	74.269997
4/1/2015	82.279999	78.050003
3/2/2015	83.93	82.25
2/2/2015	84.790001	83.93
1/2/2015	86.269997	84.980003
12/1/2014	86.720001	85.879997
11/3/2014	76.349998	87.540001
10/1/2014	76.510002	76.269997
9/2/2014	75.419998	76.470001
8/1/2014	73.32	75.5
7/1/2014	75.269997	73.580002
6/2/2014	76.580002	75.07
5/1/2014	79.730003	76.769997
4/1/2014	76.760002	79.709999
3/3/2014	74.489998	76.43
2/3/2014	74.190002	74.699997
1/2/2014	78.720001	74.68
12/2/2013	80.889999	78.690002
11/1/2013	76.970001	81.010002
10/1/2013	73.870003	76.75
9/3/2013	73.480003	73.959999
8/1/2013	78.419998	72.980003
7/1/2013	74.989998	77.940002
6/3/2013	75.059998	74.489998
5/1/2013	77.849998	74.839996
4/1/2013	75	77.720001
3/1/2013	70.779999	74.830002
2/1/2013	70.110001	70.779999
1/2/2013	68.93	69.949997
12/3/2012	72.110001	68.230003
11/1/2012	75.129997	72.019997
10/1/2012	73.800003	75.019997
9/4/2012	72.769997	73.800003
8/1/2012	74.699997	72.599998
7/2/2012	69.599998	74.43
6/1/2012	65.43	69.720001
5/1/2012	58.950001	65.82
4/2/2012	61.080002	58.91
3/1/2012	59.360001	61.200001
2/1/2012	61.790001	59.080002
1/3/2012	59.970001	61.360001
12/1/2011	58.639999	59.759998
11/1/2011	55.82	58.900002
10/3/2011	51.880001	56.720001
9/1/2011	53.200001	51.900002
8/1/2011	52.790001	53.189999
7/1/2011	53.189999	52.709999
6/1/2011	54.98	53.139999
5/2/2011	55.080002	55.220001
4/1/2011	52.25	54.98
3/1/2011	52.16	52.049999
2/1/2011	56.369999	51.98
1/3/2011	54.23	56.07
12/1/2010	54.419998	53.93
11/23/2010	54.200001	54.09