To solve this problem, let us first assign some variables.
Let us say that:
d = represents the population density of the circular region
(in units of 513 people per square mile)
p = represents the population of the circular region (in
units of people)
r = is the radius of the circular region
Now we can see that if we divide p by d, we can get a value
which has a units of square mile. Thus the area of the region, hence:
Area = 79,000 people / (513 people per square mile)
Area = 154 square mile
The area of a circle has the formula:
Area = π r^2
Therefore calculating for r:
154 square mile = π r^2
r = 7 miles (ANSWER)
