Grade 6 · Unit 3Topic 2 of 3~13 min

Writing Algebraic Expressions

Turn word phrases into math, then plug in numbers to evaluate.

Step 1 · Learn

Walkthrough

Read this first — it covers the idea in plain language with a worked example.

A variable is a letter that stands for an unknown number. "Five more than a number" becomes n + 5. "Three times a number, minus 7" becomes 3n − 7.

To evaluate, substitute the given value for the variable and simplify using the order of operations.

Worked example

Evaluate 2x + 5 when x = 4.

Tip

Watch the order of the words: "7 less than a number" is n − 7, not 7 − n.

Step 2 · Watch

Watch the main video, then check the second take if you want another explanation.

Khan Academy

Turn word phrases like "five more than x" into algebra.

Math Antics

Why letters stand for unknown numbers in math.

Step 3 · Practice

Try a worksheet or work through some problems before the quiz.

Step 4 · Check

A couple of questions to make sure this topic stuck. Retake as many times as you want.

Writing Algebraic Expressions

Easy

Write an expression for "twice a number plus 9."