PSAT Math Multiple-Choice Question 469: Answer and Explanation

Question: 469

A car's fuel economy generally increases as its speed increases, but past a certain speed, it starts to drop, as depicted for a particular car in the graph above. What is the best estimate of this car's fuel economy, in miles per gallon, at 100 miles per hour?

• A. 0
• B. 10
• C. 17
• D. 41

Correct Answer: B

Explanation:

B

Difficulty: Easy

Category: Graphs of Quadratics

Getting to the Answer: Sketch a regression line on the graph. You'll notice it has a slight curve. Extending the regression line to the x-axis allows you to reasonably estimate what your fuel economy at 100 miles per hour (mph) will be. Notice that the miles per gallon (mpg) drop from 80 mph to 90 mph is slightly less than 10, so it is reasonable to expect a drop of another full 10 mpg as the curve steepens from 90 mph to 100 mph. Therefore, the mpg at 100 mph would be about 10, so (B) is correct.