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Thirty randomly selected seniors at Council High School were asked to report the age (in years) and mileage of their main vehicles. Here is a scatterplot of the data:

We used Minitab to perform a least-squares regression analysis for these data. Part of the computer output from this regression is shown here.

a. Explain what the value of r2tells you about how well the least-squares line fits the data.

b. The mean age of the students鈥 cars in the sample was x=5years. Find the mean mileage of the cars in the sample.

c. Interpret the value of s.

d. Would it be reasonable to use the least-squares line to predict a car鈥檚 mileage from its age for a Council High School teacher? Justify your answer.

Short Answer

Expert verified

Part a. We interpret that 77%of the variation between the variables has been explained by the least squares regression line.

Part b. The mean mileage is 105800miles.

Part c. The error made when predicting the mileage using the least square regression line is on average 22723miles.

Part d. The data of students is not representative for the teachers and thus we cannot use the least-squares line to predict the mileage of cars of teachers.

Step by step solution

01

Part a. Step 1. Explanation

It is given in the question the table in which the values are calculated. Thus, from table we have,

The value of r2is given in the output as 鈥淩-Sq鈥:

r2=77%=0.77

From this, we interpret that77% of the variation between the variables has been explained by the least squares regression line.

02

Part b. Step 1. Explanation

As we know that the least square regression line is as:

y^=a+bx

With the predicted mileage and the age.

The constant ais given in the row with 鈥淎ge鈥 and in the column with 鈥淐oef鈥:

a=-13832

The slope bis given in the row with 鈥淎ge鈥 and in the column with 鈥淐oef鈥:

b=14954

Then the least square equation then becomes:

y^=-13832+14954x

With y^the predicted mileage and xthe age.

The point (x,y)lies on the least square regression line thus the mean mileage can be obtained by replacing xby xin the least square equation and evaluating the expression:

y=y^=-13832+14954x=-13832+14954(8)=105800

Thus, the mean mileage islocalid="1664182337396" 105800.

03

Part c. Step 1. Explanation

In the question it is given the table of calculated values.

Thus, from that it is given the value of s, it is as:

s=22723

Thus, from this we interpret that the error made when predicting the mileage using the least square regression line is on average 22723 miles.

04

Part d. Step 1. Explanation

It is not be reasonable to use the least square line to predict a car鈥檚 mileage from its age for a Council high school teacher because the least-squares line was determined using data of students. The data of students is not representative for the teachers and thus we cannot use the least-squares line to predict the mileage of cars of teachers.

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