Grade 9 Math (MTH1W) · Data

Predicting with a line of best fit

Use the equation of a line of best fit to predict a value, and classify the prediction as interpolation or extrapolation. Unlimited questions, five difficulty levels, and a full worked solution every time — free.

Practice this skill Curriculum: MTH1W-D2.4, MTH1W-D2.5

Try one

A scatter plot of the temperature outside (deg C) (x) versus hot chocolate cups sold (y) has a line of best fit y = -x + 15. The data was collected for x from -10 to 15. Use the equation to predict y when x = 2, and state whether this is interpolation or extrapolation.

y is about 13 (extrapolation)
y is about 17 (interpolation)
y is about −2 (interpolation)
y is about 13 (interpolation)

Answer: y is about 13 (interpolation)

See one solved, step by step

A scatter plot of the temperature outside (deg C) (x) versus hot chocolate cups sold (y) has a line of best fit y = -1.5x + 10. The data was collected for x from -10 to 15. Use the equation to predict y when x = 8, and state whether this is interpolation or extrapolation.

y is about −12 (interpolation)
y is about −2 (interpolation)
y is about 22 (interpolation)
y is about −2 (extrapolation)

📘 Worked solution

1y = −1.5 · 8 + 10 = −2Substitute x = 8 into the line of best fit equation.

28 is between −10 and 15.Compare x = 8 to the range of the collected data.

3This is interpolation.Predicting inside the data range is interpolation — usually reliable.

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