Menu

Undoing Subtraction

Part of the Fundamentals section of Coddy's Algebra journey. Lesson 3 of 61.

Before, you subtracted 28 from both sides to undo adding 28. To undo subtracting, do the opposite: add to both sides. In a sale, a jacket costs $15 less, and you pay $47. Call the old price $x$ :

$x-15 = 47$

$x-15+15 = 47+15$

$x = 62$

Check: $62-15 = 47$ . You can also write the answer the other way round: $62 = x$ means the same as $x = 62$ .

Challenge

Find $x$ . This time it sits on the right side. Pick what to do to both sides, then work out each side. Done means $x$ is alone on one side and a number is on the other.

Try it yourself

52 = x-19

Get $x$ alone

All lessons in Fundamentals

1What an Equation Is

The Equation The Same to Both SidesUndoing SubtractionRecap: First Equations

4Two-Step Equations

Two Layers to Undo Subtract, Then Divide Add, Then Divide A Division Inside Negatives in Two Steps Recap: Two-Step Equations

7Fractions in Equations

A Fraction Coefficient Clearing One Denominator Two Denominators A Fraction Around a Sum Cross-Multiplying Recap: Fractions

10From Words to Equations

Phrases into Expressions Sentences into Equations Consecutive Numbers Age and Money A Perimeter Problem Recap: Words

3Negative Numbers

Below Zero A Negative Answer Negative Coefficients The Opposite of x Recap: Negatives

6Variables on Both Sides

x on Both Sides Gathering the x's Numbers and x's Everywhere Parentheses on One Side When x Is Negative Recap: Both Sides

9Special Cases

No Solution Always True Checking a Solution Recap: Special Cases

12Final Challenges

Parentheses on Both Sides Fractions and x's Decimals on Both Sides The Story Problem