A bacteria culture starts with 660 bacteria and grows at a rate proportional to its size. After 6 hours there will be 3960 bacteria. (a) Express the population after t hours as a function of t. population: (function of t) (b) What will be the population after 3 hours?

Respuesta :

Answer:

a) [tex] P(t) = 660 e^{\frac{ln(6)}{6} t}[/tex]

b) [tex] P(t=3) = 660 e^{\frac{ln(6)}{6}*3} = 1616.663 \approx 1617[/tex]

Step-by-step explanation:

For this case we have the following info:

[tex] P(0) = 660[/tex] represent the initial amount of bacteria

[tex] P(6) = 3960[/tex] represent the population of bacteria after 6 hours

Part a

For this case we use the proportional model given by:

[tex] \frac{dP}{dt}= kP[/tex]

Where P represent the population at time t and k is a constant of proportionality.

We can rewrite the model like this:

[tex] \frac{dP}{P} = k dt[/tex]

And if we integrate both sides we got:

[tex] ln |P|= kt + C[/tex]

Now if we apply exponential we got:

[tex] P = e^{kt +c}= e^{kt} e^C[/tex]

[tex] P(t)= P_o e^{kt}[/tex]

For this case using the initial condition:

[tex] 660 = P_o e^{0k}, P_o = 660[/tex]

We have the following model:

[tex] P(t) = 660 e^{kt}[/tex]

Using the second condition [tex] P(6) = 3960[/tex] we have this:

[tex] 3960 = 660e^{6k}[/tex]

We can divide both sides by 660 and we got:

[tex] 6= e^{6k}[/tex]

Now we can apply natural log on both sides and we got:

[tex] ln (6)= 6k[/tex]

[tex] k = \frac{ln(6)}{6}=0.2986265782[/tex]

So then the model would be given by:

[tex] P(t) = 660 e^{\frac{ln(6)}{6} t}[/tex]

Part b

For this case we just need to replace t=3 into the model and we got:

[tex] P(t=3) = 660 e^{\frac{ln(6)}{6}*3} = 1616.663 \approx 1617[/tex]