Add, Then Divide

Part of the Fundamentals section of Coddy's Math journey. Lesson 19 of 64.

4x - 7 = 9: the unknown is multiplied by 4, then 7 is taken away. Undo the subtraction first by adding 7 to both sides, then divide by 4.

4x = 16

x = 4

Check: 4 × 4 - 7 = 9. True.

Read the sign in front of the number as part of the number: the outer layer of 4x - 7 is "minus 7", and its inverse is "plus 7". Students who read it as "7" and subtract get 4x = 2 and a wrong answer that a quick substitution would have caught.

Challenge

Solve the equation 3x - 11 = 10 for x.

Try it yourself

3x - 11 = 10

Solve for x

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Fundamentals

1What an Equation Is

The Equation Finding the Unknown The Same to Both Sides Solved Means Alone Recap: First Equations

4Two-Step Equations

Two Layers to Undo Subtract, Then DivideAdd, Then DivideA 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