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9th grade · Math · Unit 2 of 18

Rearranging Formulas

Solve for any letter

What your child practices

Rearranging a formula to solve for one quantity (d = rt for t, P = 2l + 2w for l) and using it, plus justifying each step in solving an equation.

Alabama Course of Study content standard: GDA.4 · rearranging formulas to highlight a quantity of interest

How we explain it

Children can open this short lesson before they practice.

  1. Treat the other letters like numbers.
  2. Undo each operation on the letter you want, in reverse order.
  3. Do the same thing to both sides.

Example: Solve d = rt for t. t is multiplied by r. Divide both sides by r. Answer: t = d/r

Rearranging Formulas in Alabama

In the Alabama Course of Study, this is unit 2 of 18 in 9th grade Math, after Number Sets and before Lines & Intersections.

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

    Solve y = mx + b for x.

    • x = (y − b)/m
    • x = (y + b)/m
    • x = y/m − b
    • x = m(y − b)

  2. Question 2

    To solve 2x + 6 = 16, Nia first subtracts 6 from both sides. What equation comes next?

    • 2x = 16
    • 2x = 10
    • 2x = 22
    • x + 6 = 9

  3. Question 3

    Use P = 2l + 2w. A rectangle has perimeter 20 ft and width 2 ft. What is its length?

    • 10 ft
    • 16 ft
    • 18 ft
    • 8 ft

  4. Question 4

    Use d = rt. A car travels 300 miles at 50 miles per hour. How many hours does it take?

    • 15000 h
    • 7 h
    • 6 h
    • 44 h

  5. Question 5

    To solve 8x + 4 = 76, Nia first subtracts 4 from both sides. What equation comes next?

    • 8x = 80
    • x + 4 = 76
    • 8x = 76
    • 8x = 72

  6. Question 6

    Solve V = lwh for h.

    • h = Vlw
    • h = V − lw
    • h = lw/V
    • h = V/(lw)

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