Consider the multiple regression model with two regressors and , where both variables are determinants of the dependent variable. you first regress y on only and find no relationship. however, when regressing y on and , the slope coefficient changes by a large amount. x1 x2 x1 x1 x2 β1 this suggests that your first regression suffers from:

The weight of a radioactive isotope was 96 grams at the start of an experiment. after one hour, the weight of the isotope was half of its initial weight. after two hours, the weight of the isotope was half of its weight the previous hour. if this pattern continues, which of the following graphs represents the weight of the radioactive isotope over time? a. graph w b. graph x c. graph y d. graph z