Testinar Grade 8 math

Building Linear Functions

Learn to reason about and solve Grade 8 problems involving Building Linear Functions.

CH04-05 Functions and Linear Relationships
Name
Date
Score
____ / 8
Directions Solve each problem. Show your reasoning on the page or on separate paper. Check the answer key only after finishing.
  1. A spring stretches when weights are attached. The table shows the length \(L\) (in cm) for a spring with \(w\) weights attached. Which equation describes the relationship?

    Building Linear Functions visual for G8-C04-T05-Q004
    1. \(L=2w+10\)
    2. \(L=10w+2\)
    3. \(L=4w+10\)
    4. \(L=w+10\)
  2. A town's population \(P\) (in thousands) at year \(t\) (years since 2010) follows this data: What is the rate of change of the population per year?

    Building Linear Functions visual for G8-C04-T05-Q005
    1. 2 thousand per year
    2. 3 thousand per year
    3. 6 thousand per year
    4. 9 thousand per year
  3. The graph shows a linear function passing through points \((0, 3)\) and \((2, 7)\). What is the slope of the line?

    Building Linear Functions visual for G8-C04-T05-Q006
    1. \(2\)
    2. \(3\)
    3. \(\frac{1}{2}\)
    4. \(\frac{2}{7}\)
  4. The graph shows a line passing through \((0, 4)\) and \((3, 10)\). What is the equation of the line?

    Building Linear Functions visual for G8-C04-T05-Q014
    1. \(y=2x+4\)
    2. \(y=3x+4\)
    3. \(y=2x+3\)
    4. \(y=4x+3\)
  5. The table shows a linear function. Find the missing \(y\) value.

    Building Linear Functions visual for G8-C04-T05-Q016
    1. \(13\)
    2. \(15\)
    3. \(14\)
    4. \(16\)
  6. The graph shows a linear function. What are the slope and \(y\)-intercept?

    Building Linear Functions visual for G8-C04-T05-Q020
    1. Slope \(=1\), intercept \(=2\)
    2. Slope \(=2\), intercept \(=1\)
    3. Slope \(=4\), intercept \(=6\)
    4. Slope \(=\frac{1}{2}\), intercept \(=4\)
  7. Using the equation \(y=3x-5\), complete the table: What is the sum of the three \(y\) values?

    Building Linear Functions visual for G8-C04-T05-Q022
    1. \(6\)
    2. \(15\)
    3. \(20\)
    4. \(25\)
  8. The graph below shows a line. Which equation represents this line?

    Building Linear Functions visual for G8-C04-T05-Q025
    1. \(y=2x-1\)
    2. \(y=x\)
    3. \(y=2x+1\)
    4. \(y=\frac{1}{2}x+\frac{1}{2}\)
Teacher and parent reference

Answer key and explanations

  1. A. \(L=2w+10\)

    Initial length is \(10\) cm (when \(w=0\)). Change from 2 to 4 weights: length goes from 14 to 18 cm, a change of 4 cm for 2 weights, so slope is \(2\). Equation: \(L=2w+10\).

  2. A. 2 thousand per year

    Slope is \(\frac{\Delta P}{\Delta t}=\frac{6}{3}=2\) thousand per year from \(t=0\) to \(t=3\) (or any consecutive pair).

  3. A. \(2\)

    Slope is \(m=\frac{y_2-y_1}{x_2-x_1}=\frac{7-3}{2-0}=\frac{4}{2}=2\).

  4. A. \(y=2x+4\)

    \(y\)-intercept is 4. Slope is \(\frac{10-4}{3-0}=\frac{6}{3}=2\). Equation: \(y=2x+4\).

  5. B. \(15\)

    Slope is \(\frac{11-7}{2-1}=4\). When \(x=3\): \(y=11+4=15\).

  6. A. Slope \(=1\), intercept \(=2\)

    \(y\)-intercept is 2 (at \(x=0\)). Slope is \(\frac{6-2}{4-0}=\frac{4}{4}=1\).

  7. A. \(6\)

    For \(x=0\), \(y=-5\). For \(x=2\), \(y=1\). For \(x=5\), \(y=10\). The sum is \(-5+1+10=6\).

  8. A. \(y=2x-1\)

    Slope: \(m=\frac{5-1}{3-1}=\frac{4}{2}=2\). Using point \((1,1)\): \(1=2(1)+b \Rightarrow b=-1\). Equation: \(y=2x-1\).

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