An Urban Density Model Is a Formula That Relates the Population

Multiple Choice

An urban density model is a formula that relates the population density D ( in thousands/ mi ² ) to the distance x (in miles) from the center of the city. The formula for the central density a and coefficient of decay b has been found to be appropriate for many large U.S. cities. For the city of Atlanta in 1970, a = 5.5 and b = 0.10. At approximately what distance was the population density 800 per square mile?

A) 39.8 mi
B) 19.3 mi
C) 21.6 mi
D) 8.4 mi
E) 49.8 mi