The National Association of Realtors (NAR) Existing-Home Sales Series provides a measurement of the residential real estate market. On or about the 25th of each month, NAR releases statistics on sales and prices of condos and co-ops, in addition to existing single-family homes, for the nation and the four regions. The data presented here indicate the number of (in thousands) existing-home sales as well as condo/co-op sales:

a. Construct the regression equation that would predict the number of condo/co-op sales using the number of single-family sales.
b. One might conjecture that these two markets (single-family sales and condo/co-op sales) would be competing for the same audience. Therefore, we would expect that as the number of single-family sales increases, the number of condo/co-op sales would decrease. Conduct a hypothesis test to determine this using a significance level of 0.05.
c. Provide a prediction interval for the number of condo/co-op sales when the number of single-family sales is 6,000 (thousands). Use a confidence level of 95%.

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Single-Family Condo/Co-op Year Month Sales Sales 2009 Apr May in Jul Aug Sept Oct Nov Dec an Fcb Mar Apr 6.270 6,230 6.330 6,220 6.280 6.290 6,180 6.150 5,860 5.790 6.050 6,040 5.920 895 912 943 914 928 908 867 876 885 781 852 862 839 2010