SAT Math Multiple Choice Practice Question 208: Answer and Explanation

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Question: 208

10. Which linear equation best models the following data?

C. y = -3x - 1
D. y = 3x - 1
E. y = 3x + 2

Correct Answer: C


C. All the equations shown are in slope-intercept (y = mx + b) form, so you need to determine the slope and the y-intercept of this line. The y-intercept happens when x is 0, so you already know that the y-intercept is -1. With this knowledge, you can eliminate Choices (B) and (E). Finding the slope is easiest if you can find two x values that are only one apart; -1 and 0 will work in this case. From the chart you can see that when x increases by 1 (from -1 to 0), the y value decreases by 3 (from 2 to -1). This allows you to determine the slope of the line: . Choice (C) is the only option with a slope (m) of -3 and a y-intercept (b) of -1. If you prefer, you can solve this problem by choosing an x-value from the chart and plugging it into each of the equations to see which ones give you the correct y-value. Make sure to check all the choices, because you may have picked an x-value that works in more than one of the choices. If that happens, all you have to do is test each of the remaining choices with a new x-value from the chart.

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