Review of straight lines. During the period after birth, a male white rat gains exactly 40 grams (g) per week. (This rat is unusually regular in his growth, but 40 g per week is a realistic rate.)

(a) If the rat weighed 100 g at birth, give an equation for his weight after x weeks. What is the slope of this line?

332 CHAPTER 15 Describing Relationships: Regression, Prediction, and Causation

(b) Draw a graph of this line between birth and 10 weeks of age.

(c) Would you be willing to use this line to predict the rat’s weight at age 2 years? Do the prediction and think about the reasonableness of the result.

(There are 454 grams in a pound. A large cat weighs about 10 pounds.)