Question

When records were first kept (t=0), the population of a rural town was 260 people. During the following years, the population grew at a rate of P'(t) = 45(1+sqrt(t)).

a) what is the population after 15 years?
b) find the popuation P(t) at any time t > 0.

Answer 1

Answer:

(a) The population after 15 years is 2678.

(b)Therefore the population P(t) at any time t>0 is

$P(t)= 45t+30 {t^{\frac32}}+260$

Step-by-step explanation:

Given that,

The population grew at a rate of

$P'(t)=45(1+\sqrt t)$

Integrating both sides

$\int P'(t) dt=\int 45(1+\sqrt t)dt$

$\Rightarrow \int P'(t) dt=\int (45+45\sqrt t)dt$

$\Rightarrow \int P'(t) dt=\int 45\ dt+\int 45\sqrt t\ dt$

$\Rightarrow P(t)= 45t+45\ \frac{t^{\frac12+1}}{\frac12+1}+c$              [ c is integration constant]

$\Rightarrow P(t)= 45t+45\ \frac{t^{\frac32}}{\frac32}+c$

$\Rightarrow P(t)= 45t+45\times\frac 23 \times {t^{\frac32}}+c$

$\Rightarrow P(t)= 45t+30 {t^{\frac32}}+c$

When t=0 , P(0)= 260

$\therefore 260= 45\times0+30\times {0^{\frac32}}+c$

$\Rightarrow c=260$

$\therefore P(t)= 45t+30 {t^{\frac32}}+260$

Therefore the population P(t) at any time t>0 is

$P(t)= 45t+30 {t^{\frac32}}+260$

To find the population after 15 years, we need to plug t=15 in the above expression.

$P(15)=( 45\times 15)+30( {15^{\frac32}})+260$

         ≈2678

The population after 15 years is 2678.