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8th grade · Math · Unit 13 of 17

Systems of Equations

Where two lines meet

What your child practices

Solving pairs of linear equations, checking a solution, telling when a system has no solution or infinitely many, and simple word problems.

Alabama Course of Study content standard: 8.12 · solving systems of two linear equations

How we explain it

Children can open this short lesson before they practice.

  1. The solution is the point that works in both equations.
  2. Set the two expressions for y equal and solve for x, then find y.
  3. Same slope, different intercept: no solution. Same line: infinitely many.

Example: Where do y = 2x + 1 and y = x + 4 meet? 2x + 1 = x + 4, so x = 3. y = 3 + 4 = 7. Answer: (3, 7)

Systems of Equations in Alabama

In the Alabama Course of Study, this is unit 13 of 17 in 8th grade Math, after Exponent Rules and before Functions.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Alabama State Department of Education (ALSDE)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Where do the lines y = −3x + 4 and y = −4x + 5 meet?

    • (1, 2)
    • (−1, 1)
    • (1, 1)
    • (2, −2)

  2. Question 2

    Two numbers add to 13. Their difference is 1. What are the numbers?

    • 7 and 6
    • 6 and 7
    • 8 and 5
    • 13 and 1

  3. Question 3

    Adult tickets cost $10 and child tickets $2. 14 tickets cost $92 in all. How many adult tickets were sold?

    • 8
    • 6
    • 9
    • 7

  4. Question 4

    Is (−1, 7) a solution of both y = 4x + 11 and y = x + 5?

    • Yes, it works in both
    • No, it only works in the first
    • No, it works in neither

  5. Question 5

    How many solutions does this system have? y = −x − 3 and y = −x − 2

    • Exactly one solution
    • No solution
    • Infinitely many solutions

  6. Question 6

    Is (−5, −4) a solution of both y = −3x − 19 and y = x + 1?

    • No, it works in neither
    • No, it only works in the first
    • Yes, it works in both

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