I'm not sure what you meant after alligators, if it was or or for, but I think it was for so I'm going with that. If 60 increase every 5 years, it would be 60 over 5 (in fractions). So I would do 60 divided by 5, which would be 12. So that means 12 increase every year. I'm not sure what mean meant either, if you're talking about the mathematical mean, but you can't solve the mean in this problem. The Answer: The yearly change in the alligator population would be 12.
