Variables and Expressions
Letters stand for unknown or changing numbers in expressions.
Key idea
Letters stand for unknown or changing numbers in expressions.
In depth
A variable is a letter standing in for a number that can change or is unknown. An expression combines numbers, variables and operations without an equals sign. Algebra lets you describe a pattern once and use it for every value.
Worked example
If a pen costs p and you buy 3, the cost is 3p. For p = 2 that is 6.
Formula
Real-world uses
- Writing a phone plan cost as 10 + 0.5m for m minutes
- Spreadsheet formulas
- General rules in science
Common mistake
Treating an expression like an equation. 3p + 2 is not something you solve; you can only simplify or evaluate it.
How to learn this
- Read the key idea and say it in your own words.
- Work through the worked example, then try a similar problem.
- Use the interactive lesson’s visual and mini-quiz to check the pattern.
Frequently asked questions
What is Variables and Expressions?
Letters stand for unknown or changing numbers in expressions. It is a topic at the beginner level in Algebra.
What is the formula for Variables and Expressions?
The key formula is 3x + 2.
Where is Variables and Expressions used in real life?
Real-world examples: Writing a phone plan cost as 10 + 0.5m for m minutes; Spreadsheet formulas; General rules in science.
What should I learn before Variables and Expressions?
It is the first topic in Algebra, so no earlier topic in this area is needed.
What is a common mistake with Variables and Expressions?
Treating an expression like an equation. 3p + 2 is not something you solve; you can only simplify or evaluate it.
How can I practise Variables and Expressions?
Open the interactive lesson, play with the visual, then answer the three-question mini-quiz. Getting two right marks the topic complete.
What comes after Variables and Expressions?
Move on to Evaluating Expressions next.
Related beginner topics in Algebra
- Evaluating Expressions – Substitute values for variables and simplify.
- Like Terms – Terms with the same variable part can be combined.
- Distributive Property – Multiplication spreads over addition.
- Simplifying Expressions – Combine like terms and apply distribution to write expressions compactly.
- Writing Expressions from Words – Translate phrases like “three more than twice a number” into algebra.
- One-Step Equations – Undo one operation to isolate the variable.