Question the-st

3.4 Two-Variable Data & Models - Line of best fit
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  • The sterplot has 10 data points.
  • The data points are in a linear pattern trending up from left to right.
  • A line of best fit is shown:
    • The line of best fit slants up from left to right.
    • The line of best fit passes through the following approximate coordinates:
      • (0 comma 11.9)
      • (12 comma 30.3)
      • (20 comma 42.6)

The sterplot shows the relationship between two variables, x and y , for data set E. A line of best fit is shown. Data set F is created by multiplying the y-coordinate of each data point from data set E by 3.9 . Which of the following could be an equation of a line of best fit for data set F?

A.

y=46.8+5.9x

B.

y=46.8+1.5x

C.

y=12+5.9x

D.

y=12+1.5x

The sterplot has 10 data points. The data points are in a linear pattern trending up

Hard-difficulty · SAT Math · Two-Variable Data & Models — Line of best fit. Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.

Answer explanation

Choice A is correct. An equation of a line of best fit for data set F can be written in the form y=a+bx, where a is the y-coordinate of the y-intercept of the line of best fit and b is the slope. The line of best fit shown for data set E has a y-intercept at approximately 0,12. It's given that data set F is created by multiplying the y-coordinate of each data point from data set E by 3.9 . It follows that a line of best fit for data set F has a y-intercept at approximately 0,123.9, or 0,46.8. Therefore, the value of a is approximately 46.8 . The slope of a line that passes through points x1,y1 and x2,y2 can be calculated as y2-y1x2-x1. Since the line of best fit shown for data set E passes approximately through the point 12,30, it follows that a line of best fit for data set F passes approximately through the point 12,303.9, or 12,117. Substituting 0,46.8 and 12,117 for x1,y1 and x2,y2, respectively, in y2-y1x2-x1 yields 117-46.812-0, which is equivalent to 70.212, or 5.85 . Therefore, the value of b is approximately 5.85 , or approximately 5.9 . Thus, y=46.8+5.9x could be an equation of a line of best fit for data set F.

Choice B is incorrect and may result from conceptual or calculation errors.

Choice C is incorrect and may result from conceptual or calculation errors.

Choice D is incorrect. This could be an equation of a line of best fit for data set E, not data set F.