SAT Math Multiple Choice Question 391: Answer and Explanation

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Question: 391


The Florida Department of Wildlife caught and tagged 10 adult female alligators as part of an effort to protect this endangered species. They took various measurements and readings related to body size and health. The total body length is plotted against the tail length in the scatterplot shown above, along with a line of best fit. Which of the following equations best models the data?

  • A. y = 0.5x
  • B. y = 2x
  • C. y = 0.4x + 1
  • D. y = 0.6x - 1

Correct Answer: A



Difficulty: Easy

Category: Problem Solving and Data Analysis / Scatterplots

Strategic Advice: Don't get bogged down in the contextual information in this question. You're looking for the equation that best matches the line drawn through the data points.

Getting to the Answer: The best-fit line begins at the origin, which means the y-intercept is 0 (the b in the equation y = mx + b), so you can eliminate C and D. Now, find the slope of the line. Between (0, 0) and (8, 4), the line rises 4 units and runs 8 units, so the slope is which is equivalent to 0.5. This means (A) is correct.

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