Solve Logistic Equation: Find P(65) | Homework Due Early

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In summary, the conversation involves the speaker seeking help on a homework assignment due the following morning. They are struggling with a logistic equation and have attempted various methods to solve it, but have been unsuccessful. The speaker also mentions a second problem that they are unable to understand. They eventually receive help and solve the first equation, but are still struggling with the second.
  • #1
CookieSalesman
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5
Would really appreciate some help on this. Homework is due really early in the morning tomorrow, and I've been trying at this for a few hours to no avail.

I have a logistic equation, (sorry, I just cannot use latex)
dP/dT = (.00777777)P(9-P)
(For P positive)

Assume P(0)=2
I must find P(65) or t=65
I've solved this many times over and over, and I continuously get different answers. I'm not sure if I'm not even supposed to solve this, but here's what I try-
I separate variables, and try to integrate this equation. Partial fractions, logarithms, etc, then I find C.
I'm not posting the steps because I've done them at least ten times all different, somehow, but perhaps I'm not supposed to be solving for this?

Anyhow I guess I try to find an equation for P(t) without derivatives- I get constants for C like 7/2, 2/7, other random numbers, not once does it ever work out well.This seems simple enough, just integrate the whole thing, but it really is just impossible for me. However one thing I do the same each time through is to separate variables, one side is 1/P(9-P) dP, the other side is 7/900 dt...
After partial fractions, the rest just goes all weird.I have a second problem I hope someone can help with, I just took a picture of the problem...
http://postimg.org/image/tcscajp83/
Yeah, I know it's standard here for the OP to show as much work as possible, but I kid you not I have spent hours on these problems and I cannot understand them. This second problem I cannot even begin to even try.

Help would be much appreciated.
 
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  • #2
I solved the first equation and I got the solution 9/[3.5 Exp(-7t)+1], at t=65 this is basically 9.

For the second question you have to again solve the logistics equation with K=4300 (The upper case K), and P(0)=300.
After you solve this, you will get P(t)= 12900/[40 Exp(-kt)+3]. Now the question states that the population tripled in the first year, this means that

P(1)=3P(0)=900, so

12900/[40 Exp(-k)+3]=900, this gives k=1.26113
 

What is a logistic equation?

A logistic equation is a mathematical model that describes how a population grows or declines over time. It takes into account limiting factors, such as resources and competition, and predicts the population's carrying capacity, or maximum sustainable size.

How do you solve a logistic equation?

To solve a logistic equation, you need to know the initial population size, the growth rate, and the carrying capacity. Then, you can use the equation P(t) = K / (1 + Ae^(-rt)) to calculate the population size at any given time t. This equation can be solved using algebraic methods or by using a graphing calculator.

What is P(65) in a logistic equation?

P(65) represents the predicted population size at a specific time, in this case, 65 units of time. It is the dependent variable in the logistic equation and can be calculated using the equation P(65) = K / (1 + Ae^(-rt)).

What does the value of P(65) tell us?

The value of P(65) tells us the predicted population size at a specific time, in this case, 65 units of time. It can be used to track population growth or decline and make predictions about the population's future size.

Why is this topic important?

Understanding and solving logistic equations is important in many fields, including ecology, economics, and epidemiology. It allows us to make predictions about population growth or decline and understand the impact of limiting factors on a population. This knowledge can inform decision-making and help us better manage resources and plan for the future.

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