Fitting and Using a Line Worksheets, Grade 8 (8.SP.A.2) – Free PDF + Answer Key

First page of the fitting and using a line practice worksheet

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PDFs print on US Letter paper. Free for classroom and home use.

Step-by-step math videos on the Math With Mr DJ YouTube channel →

Key idea

Fit a line only to a roughly linear pattern. Judge by the vertical gaps: small, and on both sides all along. Slope = a rate with two units. Intercept = the prediction at x = 0, if that means anything. Predictions outside the data are uncertain.

Sample problems

What should you check about a scatter plot BEFORE fitting a straight line?
Using y = 8x + 25, predict the score at 3 hours and at 7 hours.
The actual scores at 3 and 7 hours were 48 and 74. Work out how far each is from your prediction.
For a line relating a plant's age in weeks (x) to its height in cm (y), the slope is 3. Interpret it.

Common mistakes to watch for

Wrote “the slope is 8” or “it goes up by 8”. Neither names what is going up or per what, and the units are what turn the number into something a student could act on.
Said “the line starts at 25” without saying what x = 0 means. The interpretation is about no revision, not about where the line meets an axis.
Gave both numbers without judging them, or said 40 is fine because the arithmetic works. The arithmetic always works — the question is whether the model still describes anything, and 345 out of 100 answers it.

The answer key explains each one, so you can tell what a wrong answer means.

How to use this set

Teach with the slides (about 15 minutes), or watch the video together.
Practice with the worksheet. Questions climb from fluency to application to reasoning.
Check understanding with the exit ticket, and send the homework home.
Mark with the answer key — each answer shows the steps and the most likely mistake.