13.1 Introduction
The following table and scatter plot show the relationship between the price (in $1,000) and the age (in years) of 15 used cars of a particular make and model.
Table 13.1: Age and Price of Used Cars

Exercise: Can We Use a Simple Linear Regression?
 Could we use a straight line to model the relationship between the price and age of the used cars?
 How does the price of used cars change when the age increases?
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Answers:
 Yes, since the points are roughly on a straight line.
 The price of used cars tends to decrease as age increases.