Rearranging formulas – Grade 9 math lesson

Lesson 9 of 17 in the Grade 9 math course

US version. US grades, US spelling and dollars ($). · UK Maths Department

A complete 45-minute lesson for grade 9 (ages 14–15) that runs on this page – at school or at home. Every answer is graded right away, with a worked explanation.

Time: 45 minutes + 20 min homework
Grade: Grade 9 (ages 14–15)
You need: Paper, a pencil and this page
Graded: Instantly, with explanations

For parents: how to use this lesson

You don't need to know this topic yourself. The lesson explains each step on screen, one tidy step at a time. Every answer is graded straight away with a worked explanation, so you never have to grade anything.

Read what your child will learn and the big ideas together.
Press Start the lesson below and sit with your child for the teaching and the worked examples (about 19 minutes).
Let them do the practice on their own. They choose Getting started, On track or Challenge – start on On track and move up after a few right in a row.
Finish with the exit ticket and the talk question: “How can you check a rearranged formula is right?”
Later that day or the next day: the homework (20 minutes), then a practice test.

Watch out for

Dividing only part of one side. Divide the whole side: use parentheses or a fraction line.
Undoing the operations in the wrong order. Undo the last thing that was done to the letter first.

Tip for home: Rearrange a formula for converting temperatures.

What your child will learn

Learning goal: solve a formula for one of its variables.

Success looks like

I can rearrange a one-step formula.
I can rearrange a two-step formula.
I can rearrange formulae with powers.

Key words

subject: the variable on its own
rearrange: change the form of a formula
inverse operation: an operation that undoes another
formula: a rule linking quantities

What to have ready

Paper and a pencil
This page on a computer, tablet or phone
For the hands-on part: Rearrange the formula for speed to find distance, then time, and check with numbers.

The big ideas (for the adult)

Changing the subject means rearranging a formula so a different letter is on its own.

Use inverse operations, as when solving an equation: from v = u + at, subtract u, then divide by t to get a = (v − u)/t.

If the letter you want is squared, take the square root as the last step.

The lesson, step by step

45 minutes in 5 parts
Part	Time	How it is checked
Starter: quick recall	5 min	Graded by Classfern
Teaching input	10 min	Not assessed, self-checked
Worked examples and guided practice	9 min	Not assessed, graded by Classfern
Independent practice	15 min	Graded by Classfern
Closure and exit ticket	6 min	Graded by Classfern, self-checked

Starter, "your turn", practice and exit ticket are graded by Classfern. Worked examples and teaching are not assessed. The hands-on task and the reflection are self-assessed. Explanations in talk are judged by the parent and not recorded.

The lesson

It runs here on the page. No sign-up and no names – progress is kept only in this browser.

Homework and practice at home

20 minutes: 10 practice questions, 3 multiple-choice questions and 2 to remember from earlier work, then a short reflection. New questions every time, all graded instantly.

More practice

Algebra 1: Linear Equations and Inequalities Practice TestGraded instantly

All Grade 9 math lessons and tests · Math Department

More Grade 9 math lessons

Curriculum

Common Core State Standards HSA.CED.A.4: “Rearrange formulas to highlight a quantity of interest, using the same reasoning as in solving equations. For example, rearrange Ohm's law V = IR to highlight resistance R.”

Common Core State Standards HSA.REI.B.3: “Solve linear equations and inequalities in one variable, including equations with coefficients represented by letters.”

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