# Years Lapsed Problem

#### lisac31

##### New Member
Hello -

I'm at a loss as to how to figure this out. Right now I'm studying how to determine the correct model to use whether it be Linear, Exponential, Log, or Power.

Here is the problem:

A rare species of bird has been re-introduced to a national forest, and researchers have been modeling their population growth over a span of 10 years. In the equation below, the variable “Years Elapsed” represents the number of years since the birds have been re-introduced to this forest. The analysts did not include the value 0 in the model, so the values for years elapsed range from 1 to 10.

(Birds) = 218.86 + 35*In(Years Elapsed)

On average, every three years the bird population increased by what?
Not sure what I'm missing. Do I use Algebra, try to plot? Thanks so much for the help.

#### obh

##### Active Member
Hi Lisa,

Is this homework? or do you have data?
Please draw a chart. What do you see?

#### lisac31

##### New Member
No, not homework. I think I figured it out using the Log equation: y=a+b*In(x) ~35*1.09=38.15 which I believe is the overall change in y.

#### obh

##### Active Member
Please try to calculate the change from year 7 to year 10 ...

#### lisac31

##### New Member
Upon further investigation looks like 38 doesn't seem to be the answer. I'm good now though as I have other examples that I'm going to review. Thanks for replying!

#### obh

##### Active Member
So what is your conclusion Lisa?

#### lisac31

##### New Member
Thanks Joeb. I'll have to review yours. My final answer was 24 but I don't have a way of verifying. The 80.59 is subtracting year 10 from year one.