November 7th, 2017, 04:31 AM  #1 
Member Joined: May 2015 From: Australia Posts: 78 Thanks: 7  exponential growth
In 1923, koalas were introduced to Kangaroo Island. In 1996, the population was 5000. By 2005, the population had grown to 27000, prompting a debate on how to control their growth and avoid koalas dying of starvation. Assuming exponential growth, find the continuous rate of growth of the koala population between 1996 and 2005. Find a formula for the population as a function of the number of years since 1996, and estimate the population in the year 2020. My answer: 1996 to 2005 = 9 years Exponential growth model: Q(t) = (Qo)(e^kt) Q(t) = 5000e^kt 27,000 = 5000e^k9 5.4 = e^k9 ln(5.4) = 9k k=0.1874 Q(t) = 5000e^0.1874t Q(24) = 5000e^0.1874(24) = 449,007 is the population in year 2020. As above, my answer addresses the question 'Find a formula for the population as a function of the number of years since 1996, and estimate the population in the year 2020.' However, I'm not sure how to answer the question 'Assuming exponential growth, find the continuous rate of growth of the koala population between 1996 and 2005.' If anyone can help, I would greatly appreciate it! Last edited by skipjack; November 7th, 2017 at 09:51 PM. 
November 7th, 2017, 05:37 AM  #2 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,580 Thanks: 1038 
Not sure what you're doing... P = Present value (5000) F = Future value (27000) n = number of years (9) r = rate (?) Formula: r = (F / P)^(1 / n)  1 r = (27000 / 5000)^(1 / 9)  1 = ~.2061 Somehow you got ~.1874 
November 7th, 2017, 02:54 PM  #3 
Member Joined: May 2015 From: Australia Posts: 78 Thanks: 7 
In the textbook, they give very brief solutions. For this question, they wrote: k=[ln(27000/5000)]/9 = 0.1874 P(t)=5000e^(0.1874t) P(24)=449,007 From what I learnt in class, k = elimination rate constant But I'm not sure how to answer the 'Assuming exponential growth, find the continuous rate of growth of the koala population between 1996 and 2005' part of the question. Last edited by skipjack; November 7th, 2017 at 09:46 PM. 
November 7th, 2017, 03:56 PM  #4 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,580 Thanks: 1038  

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