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Killing bacteria Expose marine bacteria to X-rays for time periods from 1to 15minutes. Here is a scatterplot showing the number of surviving bacteria (in hundreds) on a culture plate after each exposure time:


a. Below is a scatterplot of the natural logarithm of the number of surviving bacteria versus time. Based on this graph, explain why it would be reasonable to use an exponential model to describe the relationship between the count of bacteria and the time.


b). Here is the output from a linear regression analysis of the transformed data. Give the equation of the least-squares regression line. Be sure to defne any variables you use.

c. Use your model to predict the number of surviving bacteria after 17minutes.

Short Answer

Expert verified

a). The scatter plot does not have much curvature.

b). The equation of the least-squaresegression line is lny^=5.97316-0.218425x.

c). The expected number of bacteria after 17 minutes is 9.58247 hundred bacteria or 958.247 bacteria.

Step by step solution

01

Part (a) Step 1: Given Information

Given data:

02

Part (a) Step 2: Explanation

The scatter plot does not have much curvature, a linear model between the two variables of the scatter plot would be appropriate. As a result, using a linear relationship between ln(count)and time is reasonable.

ln(count)=a+b(time)

Taking the exponential

count=eln(count)=ea+b(time)=eaeb(time)
03

Part (b) Step 1: Given Information

Given data:

04

Part (b) Step 2: Explanation

General equation of a least square regression line:

y^=b0+b1x

In the row "constant" and the column "Coef" of the computer's output, the calculated constant b0is given.

b0=5.97316

In the row "Time" and the column "Coef" of the computer output, the slope b1is found.

b1=-0.218425

05

Part (b) Step 3: Explanation

Substituting the value of b0and b1:

y^=b0+b1x

y^=5.97316-0.218425x

Where xrepresents the current time and yis the ln (count)

lny^=5.97316-0.218425x
06

Part (c) Step 1: Given Information

Given data:

07

Part (c) Step 2: Explanation

Substituting the value of x:

lny^=5.97316-0.218425x

lny^=5.97316-0.218425(17)

lny^=2.259935

Taking the exponential

y^=elny^

=e2.259935

=9.58247

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