SAT Math Multiple Choice Question 443: Answer and Explanation
Tetanus is an infection of the body's nervous system. It is usually contracted by cutting oneself on a rusty metal object. In 2002, Country A started requiring students to have tetanus shots before entering public school. That same year, Country B started providing the vaccine free of charge to school-age children but has not required that they get it. The graph above shows the incidence rate of tetanus in these two countries starting in 2002. Which of the following statements is true?
- A. Country A's vaccine requirement had a greater impact on the incidence rate than did Country B's free vaccines.
- B. Country B's free vaccines had a greater impact on the incidence rate than did Country A's vaccine requirement.
- C. Country A's vaccine requirement had about the same impact on the incidence rate as did Country B's free vaccines.
- D. Because the countries started with different incidence rates, it is impossible to determine which country's actions had a greater impact.
Correct Answer: A
Category: Heart of Algebra / Linear Equations
Strategic Advice: Compare the differences in the two lines to the statements in the answer choices. Pay careful attention to which line represents each country.
Getting to the Answer: The lines both have different y-intercepts and different slopes. The dashed line (Country B) starts lower and has a more gradual slope, while the solid line (Country A) starts higher and has a steeper slope. This means that, even though the incidence rate was initially higher, Country A's vaccine requirement had a greater impact on the incidence rate than Country B's free vaccines. You can also think about it logically: The incidence rate in Country A started higher and ended lower than in Country B, which means there was a greater change.