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Cogito

Grade 8 Math · Chapter 10 · Lesson 2

Practice Worksheet

The Line of Best Fit

A straight line through a cloud of points.

10 problems · about 19 minutes · 8.SP.A.2, 8.SP.A.3

NameDate

Figure — use these to answer the problems

Move the line until it sits as close as it can to all the points.
-10-10-5-5551010
y = 2x
Slope2
Intercept0
Figure 1

Warm-Up Review

From earlier lessons. Loosen up before the new work.

3 problems

  1. From “Scatter Plots and Association”

    Fitted line y = 2x + 3. Predict for x = 6.

    Answer

  2. From “Volume of Cones, Cylinders, and Spheres”

    A cylinder holds 210. Its matching cone holds?

    Answer

  3. From “Distance Between Two Points”

    From (0, 0) to (8, 15). Distance?

    Answer

Warm Up

Straightforward practice. Get the method working first.

3 problems

  1. y = 5x + 2. What is y at x = 3?

    Answer

  2. y = 2x + 1. What is y at x = 6?

    Answer

  3. Must a line of best fit pass through a data point? 1 for yes, 0 for no.

    Answer

Build It Up

The same ideas with more to keep track of.

2 problems

  1. A slope of 4 on a cost-against-items plot. Cost per item?

    Answer

  2. Is predicting far outside the data reliable? 1 for yes, 0 for no.

    Answer

Stretch Yourself

Mixed problems. Work out what kind of question it is before you start.

2 problems

  1. The Prediction

    A line of best fit is y = 3x + 5. What is y when x is 4?

    Answer

  2. The Starting Value

    Same line. What is y when x is 0?

    Answer