The following table gives data collected by a convenience store chain for 20 of its stores.

Column 1: ID number for each store 

Column 2: Annual sales for the store for the previous year in thousands of dollars 

Column 3: Average number of vehicles that pass the store each day, based on actual traffic counts for one month 

Column 4: Total population that lives within a two-mile radius of the store, based on 1990 census data 

Column 5: Median family income for households within a two-mile radius of the store, based on 2000 census data 

Answer the following:

a. Which of the other three variables is the best predictor of sales? Compute correlation coefficients to answer the question.

b. Do the following regressions:

(1) Sales as a function of average daily traffic 

(2) Sales as a function of population in a two-mile radius

c. Interpret the results of the two regressions.

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Store ID No. 1 2 3 4 567 2 9 10 11 12 13 14 15 16 17 18 19 20 Annual Sales (thousands of dollars) $1,121 $ 766 $ 595 $899 $915 $782 $833 $571 $ 692 $1,005 $589 $ 671 $ 903 $703 $556 $ 657 $1,209 $ 997 $844 $883 Average Daily Traffic 61,655 35,236 35,403 52,832 40,809 40,820 49,147 24,953 40,828 39,195 34,574 26,639 55,083 37,892 24,019 27,791 53,438 54,835 32,916 29,139 Population in 2-Mile Radius 17,880 13,742 19,741 23,246 24,485 20,410 28,997 9,981 8,982 18,814 16,941 13,319 21,482 26,524 14,412 13,896 22,444 18,096 16,458 16,609 Average Income in Area $28,991 $14,731 $8,114 $15,324 $11,438 $11,730 $10,589 $10,706 $23,591 $15,703 $9,015 $10,065 $17,365 $ 7,532 $ 6,950 $ 9,855 $21,589 $22,659 $12,660 $11,618