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9th grade · Math · Unit 15 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.

California Content Standards learning standard: A-CED.4; A-REI.1 · rearranging formulas and equations to highlight a quantity

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

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

    To solve 2x + 14 = 30, Zoe first subtracts 14 from both sides. What equation comes next?

    • 2x = 16
    • x + 14 = 16
    • 2x = 30
    • 2x = 44

  2. Question 2

    Solve y = mx + b for x.

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

  3. Question 3

    Use P = 2l + 2w. A rectangle has perimeter 32 ft and width 4 ft. What is its length?

    • 16 ft
    • 28 ft
    • 12 ft
    • 24 ft

  4. Question 4

    To solve 4x + 1 = 21, Jay first subtracts 1 from both sides. What equation comes next?

    • 4x = 21
    • 4x = 20
    • 4x = 22
    • x + 1 = 21

  5. Question 5

    Use A = ½bh. A triangle has area 15 cm² and base 6 cm. What is its height?

    • 5 cm
    • 30 cm
    • 7 cm
    • 2.5 cm

  6. Question 6

    Solve F = 1.8C + 32 for C.

    • C = 1.8(F − 32)
    • C = (F − 32)/1.8
    • C = F/1.8 − 32
    • C = (F + 32)/1.8

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