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ACT® · Math: Integrating Essential Skills

Writing Algebraic Expressions

Writing algebraic expressions means translating an English phrase into math symbols in the right order. Most lost points come from reading order, not algebra, especially with "less than" and "more than."

The algebra in these problems is usually easy: add, multiply, divide. The expensive part is translation. Every phrase has a verb that tells you the operation and an order that tells you what goes where. 'Times' and 'more than' usually read in the same order you hear them, but 'less than' flips. Get the order wrong and the whole answer is wrong even though your arithmetic is fine.

The fix is to find the operation word first, then ask which quantity is doing the action to which. 'X more than y' means y + x. 'X less than y' means y - x, not x - y, because the amount 'less' is the one being removed from the other. 'Times' just multiplies in either order since multiplication doesn't care about order, so that one is safe. Once the phrase is correctly translated, you build the full expression piece by piece: a fixed cost stays a plain number, a cost that depends on an amount gets multiplied by a variable, and separate pieces that both apply get added.

This skill sits right before multi-step rate and cost problems. Once you can write the expression, the next move is almost always to plug in a number, solve for a variable, or work backward from a total, like figuring out how many hours a budget buys. The expression is the setup; everything after it is routine arithmetic, so a clean, correctly ordered expression is what makes the rest of the problem painless.

Key terms

Expression
A math phrase built from numbers, variables, and operations, with no equals sign.
Variable
A letter standing in for an unknown or changing quantity, like h for hours.
Coefficient
The number multiplied by a variable, such as the 8 in 8h.
Constant
A fixed number in an expression that doesn't change, like the 15 dollar deposit.

Watch it explained

  1. How it worksHow do the phrases more than, less than and times each map onto one symbol and one order?
  2. Common mistakeWhy isn't 5 less than x written as 5 minus x?
  3. Worked exampleFind an expression for renting a bike for h hours at 8 dollars an hour plus a 15 dollar deposit.

Check yourself

Your turneasy1 of 3
A bike rents for 10 dollars an hour plus a 16 dollar deposit. Write an expression in h for the cost of renting it for h hours.

End of topic.