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The table below shows the population of a fictional California Gold Rush town named Lehi in the years after its peak population in 1880.

[tex]\[
\begin{tabular}{|c|r|r|r|r|r|r|}
\hline
Year & 1880 & 1890 & 1900 & 1910 & 1920 & 1930 \\
\hline
Population & 8200 & 3444 & 2378 & 1575 & 690 & 315 \\
\hline
\end{tabular}
\][/tex]

For the purpose of this problem, let [tex]$P$[/tex] represent the population of Lehi [tex]$t$[/tex] years after 1880 ([tex]$t=0$[/tex] represents 1880). The new table is:

[tex]\[
\begin{tabular}{|c|r|r|r|r|r|r|}
\hline
$t$ & 0 & 10 & 20 & 30 & 40 & 50 \\
\hline
$P(t)$ & 8200 & 3444 & 2378 & 1575 & 690 & 315 \\
\hline
\end{tabular}
\][/tex]

1. Use your calculator to determine the exponential regression equation that models the set of data above. Round the "a" value to two decimals, and round the "b" value to three decimals. Use the indicated variables and proper function notation.

[tex]\( P(t) = \square \)[/tex]

2. Based on your regression model, what is the percent decrease per year?

[tex]\(\square \%\)[/tex]

3. Find [tex]\(P(35)\)[/tex]. Round your answer to the nearest whole number.

[tex]\(P(35) = \square\)[/tex]

4. Interpret your answer by completing the following sentence. Be sure to use units in your answer.

"The population of Lehi [tex]\(\square\)[/tex] years after 1880 was about [tex]\(\square\)[/tex]."

5. How long did it take for the population of Lehi to reach 370 people? Round your answer to the nearest whole number.

[tex]\(P(t) = 370\)[/tex] when [tex]\(t = \square\)[/tex]

6. Interpret your answer by completing the following sentence. Be sure to use units in your answer.

"In [tex]\(\square\)[/tex] years after 1880, the population of Lehi was about [tex]\(\square\)[/tex]."

7. How long did it take for the population of Lehi to drop by half? Round your answer to the nearest whole number.

[tex]\(P(t)\)[/tex] has halved when [tex]\(t = \square\)[/tex]

Answer :

Sure, let's work through the problem step by step.

1. Determine the Exponential Regression Equation:

To model the population of Lehi over time with an exponential function, we assume the form of the function is [tex]\( P(t) = a \cdot b^t \)[/tex].

Based on the regression model, we have:
- The "a" value is approximately [tex]\( 7849.76 \)[/tex].
- The "b" value is approximately [tex]\( 0.938 \)[/tex].

So, the equation for the model is:
[tex]\[ P(t) = 7849.76 \cdot (0.938)^t \][/tex]

2. Calculate the Percent Decrease Per Year:

The percent decrease per year is based on the value of [tex]\( b \)[/tex]:
- Since [tex]\( b \)[/tex] is approximately [tex]\( 0.938 \)[/tex], the decrease factor is [tex]\( 1 - 0.938 = 0.062 \)[/tex].

To express this as a percentage, multiply by 100:
[tex]\[ 0.062 \times 100 = 6.2\% \][/tex]

So, the population decreases by approximately 6.2% each year.

3. Find [tex]\( P(35) \)[/tex]:

To find the population 35 years after 1880:
- Substitute [tex]\( t = 35 \)[/tex] into the model:

[tex]\[ P(35) = 7849.76 \cdot (0.938)^{35} \][/tex]

The population [tex]\( P(35) \)[/tex] is approximately 911.

Interpretation:
"The population of Lehi 35 years after 1880 was about 911."

4. Determine When the Population Reaches 370:

We need to find the value of [tex]\( t \)[/tex] when [tex]\( P(t) = 370 \)[/tex]:

[tex]\[ 370 = 7849.76 \cdot (0.938)^t \][/tex]

To find [tex]\( t \)[/tex], solve the equation:
[tex]\[ t \approx 50 \][/tex]

Interpretation:
"In 50 years after 1880, the population of Lehi was about 370."

5. Determine When the Population is Halved:

The initial population is 8200. Half of this is 4100. We need to find [tex]\( t \)[/tex] when [tex]\( P(t) = 4100 \)[/tex]:

[tex]\[ 4100 = 7849.76 \cdot (0.938)^t \][/tex]

To find [tex]\( t \)[/tex], solve the equation:
[tex]\[ t \approx 11 \][/tex]

Interpretation:
"The population of Lehi halved 11 years after 1880."

These solutions provide a step-by-step explanation based on the results given. If you have further questions or need clarification on any step, feel free to ask!

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