SAT Mathematics Practice Test 5

The DBA plans to increase its membership by n businesses each year, so $\mathit{x}$ years from now, the association plans to have increased its membership by $\mathit{n}\mathit{x}$ businesses. Since there are already b businesses at the beginning of this year, the total number of businesses, $\mathit{y}$, the DBA plans to have as members $\mathit{x}$ years from now is modeled by $\mathit{y}=\mathit{n}\mathit{x}+\mathit{b}$.
Choice B is incorrect. The equation given in choice B correctly represents the increase in membership x years from now as $\mathit{n}\mathit{x}$. However, the number of businesses at the beginning of the year, b, has been subtracted from this amount of increase, not added to it. Choices C and D are incorrect because they use exponential models to represent the increase in membership. Since the membership increases by n businesses each year, this situation is correctly modeled by a linear relationship.