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The Equation

Part of the Fundamentals section of Coddy's Algebra journey. Lesson 1 of 61.

I'm thinking of a number. I add 3 and get 8. What is my number?

In algebra, we write this riddle as one line:

$x+3 = 8$

This line is an equation. An equation says that two sides are equal. The letter $x$ stands for the number we do not know yet.

Challenge

Here's my new riddle: I add 6 and get 10. Type my number.

Try it yourself

x+6 = 10

Get $x$ alone

All lessons in Fundamentals

1What an Equation Is

The EquationThe Same to Both Sides Undoing Subtraction Recap: 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