Growth rate help.

[Marconis]

We are to find the annual growth rate of a fish from 2003-2007. The measurements are taken in March and September of the same year. This is throwing me off in determining the growth rate. In general if it just said the year and then the measurement (without the two different months), I'd subtract the first year measurement from the final year measurement and divide by 4. However, when two months are involved, this doesn't seem to work. This also leads me to believe that you need to account for 5 years instead of 4. Any advice on how to go about it?

 

March 03 : 2cm

Sept. 03: 4.5cm

 

March 04: 4.7

Sept. 04: 6.6

 

March 05: 7.0

Sept 05: 9.2

 

March 06: 9.3

Sept 06: 12.0

 

March 07: 12.5

Sept 07: 16.0

[dttom]

So think about these questions:

 

What's your unit for the growth rate?

Are you looking for overall growth rate, or the instantaneous growth rate?

[Marconis]

Here's what I did:

 

To find annual growth rate, I did 16-2/10. That's 1.4cm per year, average.

 

To reach a meter in length, I did 100=1.4x, then got x=71.43. I divided that by 2 (2 months a year) and got 35.7 years.

 

Then, for average summer growth rate I did 16-4.5/5 and got 2.3cm.

 

Is this correct?

Edited September 12, 2010 by Marconis

[dttom]

I can't qutie follow what you mean, but I don't understand why you calculate the growth rate per year in (16-2)/10 (where the '10' comes from).

[Marconis]

I can't qutie follow what you mean, but I don't understand why you calculate the growth rate per year in (16-2)/10 (where the '10' comes from).

 

I just accounted for the 10 months that were used. I guess that's incorrect?

 

Hey I got help on another forum, I truly feel like an idiot for not doing it properly . Thanks anyway for responding/

[dttom]

It is 2cm in March 03 and 16cm in September 07, so the interval should be in years, not just 10 months...