Refer to Exercise 11.86. Calculate a new variable: x = 1/ density.
a. What is the interpretation of the new variable? In particular, if the new variable equals 0.50, what does that mean about the particular zip code area?
b. Plot sales against the new variable. Does a straight- line prediction look reasonable here?
c. Obtain the correlation of sales and the new variable. Compare its magnitude to the correlation obtained in Exercise 11.86 between sales and density. What explains the difference?
In exercise

Sales S4 2 54 62 72 83 115 90 66 60 100 78 152 87 54 82 Density 6.5 4.6 55 46 4.2 4.3 2.3 35 32 84 34 4.0 20 3.2 6.7 3.0 Sales 59 183 171 96 134 79 94 82 66 62 45 69 65 81 94 117 Density 5.7 13 13 3.0 2.2 43 26 3.0 43 78 94 42 5.9 6.2 2.8 24