SAT Math Multiple Choice Question 852: Answer and Explanation
12. Sea ice extent is a measurement of the area of ocean with at least 15% sea ice. Thegraph below shows data for the extent of Arctic sea ice between 2000 and 2012 as reportedby the National Snow and Ice Data Center. The line of best fit is also shown. Theequation of the line is A(t) = -0.187t + 380.5, where A(t) represents the area of measurable sea ice in the Arctic Ocean in the year t.
Based on the equation of the line of best fit, which of the following statements accuratelydescribes the change in the amount of measurable Arctic sea ice during the given timeperiod?
- A. The amount of sea ice increased approximately 187,000 square kilometers per year.
- B. The amount of sea ice increased approximately 187 million square kilometers per year.
- C. The amount of sea ice decreased approximately 187,000 square kilometers per year.
- D. The amount of sea ice decreased approximately 187 million square kilometers per year.
Correct Answer: C
Category: Problem Solving and Data Analysis / Scatterplots
Strategic Advice: In a real-world scenario, the slope of a line represents a unit rate. In this scenario, the unit rate translates as the change in the area of the sea ice per year.
Getting to the Answer: The slope of the line of best fit is -0.187. The negative slope indicates a decrease in the amount of ice, so you can eliminate A and B. To decide between (C) and D, read the vertical axis label carefully-the amount of ice is given in millions of square kilometers. Therefore, a slope of -0.187 indicates a decrease per year of 0.187 million square kilometers. This is not one of the answer choices (read D carefully), so multiply 0.187 by 1,000,000 to find that this is equivalent to a decrease of 187,000 square kilometers per year, which is (C).