A variableis a letter that stands in for a number — usually one you don’t know yet, or one that can change. When you see x, read it as “some number,” the same way you’d read a blank in a fill-in-the-blank sentence. That’s the entire idea this page is built around, and pre-algebra’s job is just to make it feel ordinary before Algebra I starts asking you to do more with it.
From word phrases to expressions
An expression is a math phrase built from numbers, variables, and operations — x + 5, for example. Translating English into expressions is most of the new skill here. “A number plus five” becomes x + 5. “Five less than a number” becomes x − 5(notice the order flips — it’s the number minus five, not five minus the number). “Twice a number” becomes 2x. Getting comfortable with these translations now is exactly what makes word problems in algebra feel manageable instead of intimidating.
Evaluating an expression
To evaluate an expression means to substitute in a specific number for the variable and simplify. If x = 4, then 3x + 2 becomes 3(4) + 2 = 12 + 2 = 14. The variable’s job is to hold a spot open; evaluating just means filling that spot in and following the order of operations from there.
Expressions vs. equations — a distinction worth making early
An expression has no equals sign — 3x + 2 — and all you can do with it is simplify or evaluate it. An equation has an equals sign — 3x + 2 = 14 — and that turns it into a claim you can check or solve. Pre-algebra usually stays mostly in expression territory, with simple one-step equations as a preview; full equation-solving is where Algebra I picks up. Keeping the two words straight now avoids confusion later.
Let me show you one
Translate and evaluate: “Take a number, add 3, then double the result” — what is it when the number is 5? First, translate: “add 3” means (x + 3), and “double the result” wraps the whole thing in multiplication by 2: 2(x + 3). Then substitute x = 5: 2(5 + 3) = 2(8) = 16. Notice the parentheses are doing real work — they keep “the result” together before doubling it.
The mistake I see most
Translating word order literally instead of meaning. “Five less than a number” gets written as 5 − x because 5 appears first in the sentence, when it should be x − 5. The fix is reading for meaning rather than word order: figure out which quantity is actually bigger or comes first in the calculation, and write the math to match that, not the sentence.
Want to work through it together?
If translating word phrases into expressions still feels uncertain, that’s the exact skill worth practicing now — it pays off the moment Algebra I starts and word problems stop being optional.
