Math Problem Statement

Karr and Coats studied the effects of several chemicals on the growth of the German cockroach. the following table gives their data for the percent of the chemical 𝛼-terpineol in the diet of 20% 𝛼-terpineol. Percent 𝛼-terpineol 1 10 25 Days to Adult Stage 129 113 115

A. On the basis of the data given in the table, find the best-fitting logarithmic function using least squares. State the square of the correlation coefficient. (Use 4 decimal places in your answer.) y(x) =

r2 =

B. Use this model to estimate the days to adult stage with a diet of 20% 𝛼-terpineol. (Round to the nearest day.) When a 20% 𝛼-terpineol, then there are days to adult stage.

Solution

To solve this problem, we'll break it down into two parts: finding the logarithmic model and using it to make predictions.

A. Finding the best-fitting logarithmic function using least squares

Given the dataTo solve this problem, we'll break it down into two parts: finding the logarithmic model and using it to make predictions.

A. Finding the best-fitting logarithmic function using least squares

Given the

Percent of 𝛼-terpineol (x):1,10,25\text{Percent of 𝛼-terpineol (x)}: 1, 10, 25 Days to Adult Stage (y):129,113,115\text{Days to Adult Stage (y)}: 129, 113, 115

We aim to find a logarithmic model of the form:

y(x)=a+bln(x)y(x) = a + b \ln(x)

We will use the least squares method to find the coefficients aa and bb. The steps include:

  1. Transform the xx values by taking the natural logarithm.
  2. Use the transformed xx values and the yy values to compute the least-squares regression.
  3. Calculate the correlation coefficient (rr) and square it to get r2r^2.

Let’s go through the calculations.

Step 1: Transform the xx values

ln(1)=0,ln(10)2.3026,ln(25)3.2189\ln(1) = 0, \quad \ln(10) \approx 2.3026, \quad \ln(25) \approx 3.2189 So, we now have the pairs: (0,129),(2.3026,113),(3.2189,115)(0, 129), (2.3026, 113), (3.2189, 115)

Step 2: Use the least squares method

The formulas for the least squares regression coefficients aa and bb are:

b=n(ln(x)y)ln(x)yn(ln(x))2(ln(x))2b = \frac{n\sum(\ln(x) \cdot y) - \sum \ln(x) \cdot \sum y}{n\sum (\ln(x))^2 - (\sum \ln(x))^2} a=ybln(x)na = \frac{\sum y - b \sum \ln(x)}{n}

where n=3n = 3 (the number of data points). I'll compute these values next.

The best-fitting logarithmic function using least squares is:

y(x)=127.93034.8521ln(x)y(x) = 127.9303 - 4.8521 \ln(x)

The square of the correlation coefficient (r2r^2) is:

r2=0.8520r^2 = 0.8520

B. Estimate the days to adult stage with a diet of 20% 𝛼-terpineol

We will use the logarithmic model to estimate the number of days to adult stage when the percent of 𝛼-terpineol is 20%.

Substitute x=20x = 20 into the equation y(x)=127.93034.8521ln(x)y(x) = 127.9303 - 4.8521 \ln(x).

Let me compute that for you.When the diet contains 20% 𝛼-terpineol, the estimated number of days to reach the adult stage is approximately 113 days.

Summary:

  • Logarithmic function: y(x)=127.93034.8521ln(x)y(x) = 127.9303 - 4.8521 \ln(x)
  • r2r^2: 0.8520
  • Estimated days for 20% 𝛼-terpineol: 113 days

Do you have any questions or need further details?

Here are some related questions to explore:

  1. What is the significance of the correlation coefficient r2r^2?
  2. How does the natural logarithmic model compare to a linear model for this data?
  3. What other types of models could be considered for this type of biological data?
  4. How would the predictions change if the diet percentage was different (e.g., 5% or 50%)?
  5. How could you experimentally verify the accuracy of this logarithmic model?

Tip: Always check the correlation coefficient (r2r^2) to assess how well a model fits the data. The closer it is to 1, the better the fit.

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Math Problem Analysis

Mathematical Concepts

Logarithmic Functions
Least Squares Regression
Correlation Coefficient

Formulas

y(x) = a + b ln(x)
r^2 = correlation coefficient squared
Least squares regression formulas for a and b

Theorems

Least Squares Method
Logarithmic Regression

Suitable Grade Level

College/Advanced High School