Problema Solution

10. A bird population is initially 150 and grows at a rate of 6% each year.

a. Find an exponential model of the form P = C ·a

t that models the bird population P, after t years.

b. Find the instantaneous growth rate r, as a percent. Round your answer to 5 decimal places.

c. Write an exponential equation of the form P = Cert for the bird population P after t years.

Answer provided by our tutors

A bird population is initially 150 and grows at a rate of 6% each year.


Since these populations grow exponentially, we are looking for a model of the form


P(t) = C*a^t, t is the time, C and a are the constants that we need to find


a. Find an exponential model that models the bird population P, after t years.


A bird population is initially 150 and grows at a rate of 6% each year.


This means that for t = 0 we have P(0) = 150 thus C*a^0 = C and C = 150


A bird population grows at a rate of 6% each year:


(P(1) - P(0))/P(0) = 0.06


P(1) - P(0) = 0.06*P(0)


150a - 150 = 150*0.06


a = (150*0.06 + 150)/150


a = 1.06


now we can write for the model of the bird population


P(t) = 150*1.06^t


b. Find the instantaneous growth rate r, as a percent. Round your answer to 5 decimal places.


To find the instantaneous growth rate differentiate the expression P(t) = 150*1.06^t


dP(t)/dt = 150*1.06^t*(ln 1.06)


r = 150*1.06^t*(ln 1.06)


r = 8.7403362*1.06^t


c. Write an exponential equation of the form P = Ce^(rt) for the bird population P after t years.


P(t) = Ce^(rt)


P(0) = 150 => C = 150


(P(1) - P(0))/P(0) = 0.06


150(e^r - 1)/150 = 0.06


e^r - 1 = 0.06


r = ln 1.06


r = 0.05827


thus the equation is


P(t) = 150 e^( 0.05827t).