5 an agricultural economist says that the correlation

5. An agricultural economist says that the correlation between corn prices and soybean prices is
r = 0 . 7. This means that
(a) when corn prices are above average, soybean prices also tend to be above average.
(b) there is almost no relation between corn prices and soybean prices.
(c) when corn prices are above average, soybean prices tend to be below average.
(d) when soybean prices go up by 1 dollar, corn prices go up by 70 cents.
(e) the economist is confused, because correlation makes no sense in this situation.

6. Which of the following statements is/are true?
I. Correlation and regression require that there are clearly-identified explanatory and
response variables.
II. Scatterplots require that both variables be quantitative.
III. Every least-squares regression line passes through ( , ). x y
7. There is an approximate linear relationship between the height of females and their age (from
5 to 18 years) described by predicted height = 50.3 + 6.01(age) where height is measured in
centimeters and age in years. Which of the following is not correct?
8. You are interested in predicting the cost of heating houses on the basis of how many rooms
the house has. A scatterplot of 25 houses reveals a strong linear relationship between these
variables, so you calculate a least-squares regression line. “Least-squares” refers to
© 2011 BFW Publishers The Practice of Statistics, 4/e- Chapter 3 127

128 The Practice of Statistics, 4/e- Chapter 3 © 2011 BFW Publishers
9. A study of the fuel economy for various automobiles plotted the fuel consumption (in liters
of gasoline used per 100 kilometers traveled) vs. speed (in kilometers per hour). A least-
squares line was fit to the data. Here is the residual plot from this least-squares fit.