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What a Variable Is

Part of the Expressions & Data section of Coddy's Pre-Algebra journey. Lesson 1 of 51.

Think of a number. Double it, add 10, halve that, then take away your number.

You got 5. How did I know?

Call your number n. A letter that stands for a number is a variable. $2n$ means 2 times n. Follow n through each step and the n goes away. So the answer is always 5.

Challenge

Try the number game with 37. Before the last step, you have $\frac{2n+10}{2}$ . Write h equal to that, with 37 in place of n. Work it out. Then take 37 away in your head.

Start the lesson to read it in the interactive player and track your progress.

All lessons in Expressions & Data

1Variables and Expressions

What a Variable IsWriting Expressions Substituting a Value Expressions from Stories Recap: Expressions

4Combining Like Terms

Like Terms Letters and Numbers Negative Terms Two Letters Distribute, Then Collect Recap: Like Terms

7Probability

Chance as a Fraction The Complement Chance as a Percent Expected Count Recap: Probability

10Final Challenges

Final: Two Brackets Final: A Cubic Expression Final: The Phone Plan Final: A Decimal Mean Final: The Last Spin

2Evaluating Expressions

Negative Inputs Powers in Expressions Formulas Recap: Evaluating

5Patterns and Sequences

Continuing a Pattern The Common Difference The nth Term Writing the Rule Recap: Sequences

8Tables and Charts

Reading a Table Totals and Differences Reading a Line Graph Percent of a Total Recap: Tables and Charts

3The Distributive Property

Number Properties Mental Math Distributing Letters Distributing a Minus Recap: Distributing

6Data and Averages

The Mean Mean with Negatives The Median The Mode The Range Recap: Data and Averages

9Perimeter and Area

Perimeter Area of a Rectangle Area of a Triangle Perimeter as an Expression Recap: Perimeter and Area