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8th grade Use the fit line's equation to predict, and say what its slope and intercept mean worksheet

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Use the fit line's equation to predict, and say what its slope and intercept mean

Grade 8 Math Worksheet

NameDate

Circle the best answer, or write your answer on the line.

  1. Kira's fit line for bean plants is y = 2.5x + 12, with x in days and y in cm. About how tall does it predict a plant is on day 8, in cm?

  2. Luz's bike fit line is y = 0.6x + 5 (x in minutes, y in km). The data stop at 35 minutes. If the pattern keeps going, about how far is a 40-minute ride?

  3. Milo's jump model is y = 1.2x + 20 (x: weeks of training, y: jumps per minute). Data end at week 45. If the pattern keeps going, about how many jumps at week 50?

  4. Pia's team drew a fit line through (2, 30) and (10, 70) on its practice plot. For each 1 more minute of practice, about how many more points does the line show?

  5. Ren's sunflower fit line passes through (4, 15) and (12, 35). For each 1 more day, about how many centimeters taller does the line show?

  6. Tala's gym class plotted minutes of exercise against heartbeats in 10 seconds. The fit line passes through (5, 12) and (25, 20). For each 1 more minute, about how many more beats does it show?

  7. Zee's baking club fit line goes through (10, 40) and (40, 100). For each 1 more minute of baking, about how many millimeters taller does the line show?

  8. Ari's class fit y = 3x + 15 to hours of practice (x) and quiz score (y). What does the 15 mean, if anything?

    • The 15 means the score tends to go up about 15 points for each extra hour.
    • The 15 means a student with 0 hours of practice tends to score about 15.
    • The 15 has no real meaning here, because no one practices 0 hours.

  9. Bo's club fit y = 1.5x + 6 to days since seedlings were moved outside (x) and height in cm (y). What does the 6 mean, if anything?

    • The 6 has no real meaning here, because no seedling is outside for 0 days.
    • The 6 means a seedling tends to be about 6 cm tall the day it goes outside.
    • The 6 means a seedling tends to grow about 6 cm each day.

  10. Jun fit y = 0.5x + 2 to park trees: trunk width in cm (x) and height in meters (y). What does the 2 mean, if anything?

    • The 2 means a tree with a trunk 0 cm wide tends to be about 2 meters tall.
    • The 2 means a tree tends to grow about 2 meters taller for each extra centimeter of width.
    • The 2 has no real meaning here, because no tree has a trunk 0 cm wide.
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8th grade Use the fit line's equation to predict, and say what its slope and intercept mean worksheet – printable
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About this worksheet

Use the fit line's equation to predict, and say what its slope and intercept mean. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can use a fit line's equation, or the line on the grid, to predict about how much y goes with an x, and the other way round.
  • I can say what the slope means in the story ("about 4 more points for each extra hour"), and whether the intercept means anything.
  • I can find a fit line's slope from two of its points, and write its equation.

Standard: 8.SP.A.3

Words to know

linear model: A fit line and its rule, used to describe and predict.

prediction: What the model says y is about, for a chosen x.

slope: How much y tends to change for each 1 more x.

intercept (start): The line's y-value at x = 0, where it crosses the y-axis.

tends to: Usually, but not exactly, for every dot.

inside / past the data: Between the smallest and largest x in the plot / just beyond it.

Common mistakes

Your child used the slope but left out the starting amount, the number added at the end of the line's rule. Read the rule together as 'start at the added number, then add the slope for each step'.

Your child swapped the two numbers of the line's rule: the slope multiplies x, and the start is added. Ask together: which number changes with each step, and which one is there at the start?

Your child read the data dot instead of the fit line. A prediction comes from the line, which shows the pattern, not from one dot. Put a finger on the line together at that spot.

Questions parents ask

What is the most common mistake with use the fit line's equation to predict, and say what its slope and intercept mean?

Your child used the slope but left out the starting amount, the number added at the end of the line's rule. Read the rule together as 'start at the added number, then add the slope for each step'.

Are these 8th grade math worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

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