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In an insect colony, there are 230 insects after 7 days. If there were initially 100 insects, how long will it take the population to grow to 600 insects?

User Apneadiving
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1 Answer

20 votes
20 votes

The population growth in this question is assumed to be exponential.

The exponential formula is given to be:


y=a(b)^x

where a is the initial amount and b is the growth rate of the population.

The question provides the following parameters:


a=100

We can find the growth rate by making the following substitution: If there were 230 insects after 7 days, we have:


x=7,y=230

Therefore,


\begin{gathered} 230=100(b)^7 \\ b^7=2.3 \\ b=\sqrt[7]{2.3} \\ b=1.126 \end{gathered}

Therefore, the exponential model for the problem is:


y=100(1.126)^x

To find the time it takes for the population to reach 600 insects, we can substitute for y = 600 into the model and solve for x:


\begin{gathered} 600=100(1.126)^x \\ 1.126^x=(600)/(100) \\ 1.126^x=6 \end{gathered}

Finding the natural logarithm of both sides:


\ln 1.126^x=\ln 6

Recall the law of logarithms:


\ln x^a=a\ln x^{}

Therefore,


\begin{gathered} x\ln 1.126=\ln 6 \\ \therefore \\ x=(\ln 6)/(\ln 1.126) \\ x=15.098\approx15 \end{gathered}

Therefore, it will take 15 days for the insect population to reach 600 insects.

User Andrei F
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