Run a regression of Walmart Sales (y) on CPI, Retail Price Index, and December.

1. Use the equation to predict Walmart's sales in a year when the CPI is 600, the retail price index is 400,000, and it is September.
2. Repeat (1) assuming the month is December. How much does the prediction change?
3. In managerially relevant terms, interpret the coefficient of December and its confidence interval.

(15 points) Can you improve the model created in number 6?If so, explain how and the fit your new model. Describe the results from your model below. How did it improve? What are the managerially relevant details?

Date	Sales ($B)	CPI	Retail Price Index	December
11/28/2003	14.764	552.7	301337	0
12/30/2003	23.106	552.1	357704	1
1/30/2004	12.131	554.9	281463	0
2/27/2004	13.628	557.9	282445	0
3/31/2004	16.722	561.5	319107	0
4/29/2004	13.98	563.2	315278	0
5/28/2004	14.388	566.4	328499	0
6/30/2004	18.111	568.2	321151	0
7/27/2004	13.764	567.5	328025	0
8/27/2004	14.296	567.6	326280	0
9/30/2004	17.169	568.7	313444	0
10/29/2004	13.915	571.9	319639	0
11/29/2004	15.739	572.2	324067	0
12/31/2004	26.177	570.1	386918	1
1/21/2005	13.17	571.2	293027	0
2/24/2005	15.139	574.5	294892	0
3/30/2005	18.683	579	338969	0
4/29/2005	14.829	582.9	335626	0
5/25/2005	15.697	582.4	345400	0
6/28/2005	20.23	582.6	351068	0
7/28/2005	15.26	585.2	351887	0
8/26/2005	15.709	588.2	355897	0
9/30/2005	18.618	595.4	333652	0
10/31/2005	15.397	596.7	336662	0
11/28/2005	17.384	592	344441	0
12/30/2005	27.92	589.4	406510	1
1/27/2006	14.555	593.9	322222	0
2/23/2006	18.684	595.2	318184	0
3/31/2006	16.639	598.6	366989	0
4/28/2006	20.17	603.5	357334	0
5/25/2006	16.901	606.5	380085	0
6/30/2006	21.47	607.8	373279	0
7/28/2006	16.542	609.6	368611	0
8/29/2006	16.98	610.9	382600	0
9/28/2006	20.091	607.9	352686	0
10/20/2006	16.583	604.6	354740	0
11/24/2006	18.761	603.6	363468	0
12/29/2006	28.795	604.5	424946	1
1/26/2007	20.473	606.348	332797	0