Question

An alligator population in a nature preserve in the everglades decreases by 60 alligators over 5 years what is the mean yearly change in the alligator population

Answer 1

 An alligator population decreases by 60 alligators over 5 years.
 60 : 5 = 12
The mean yearly change of population:
 it decreases by 12 alligators over year. 

Answer 2

The mean or average yearly change equals the total net change divided the number of years, then:

mean yearly change = total net change / # of years = 60 alligators / 5 years = 12 alligators per year.